LIBRARY 
OF  THE 

UNIVERSITY  OF  ILLINOIS 


AMERICAN  SOCIETY 


CIVIL  ENGINEERS 


THE  CONTINUOUS  TRUSS  BRIDGE 
OVER  THE  OHIO  RIVER  AT  SCIOTOVILLE,  OHIO, 

OF  THE 

CHESAPEAKE  AND  NORTHERN  OHIO  RAILWAY 


BY 

GUSTAV  LINDENTHAL,  M.  Am.  Soc.  C.  E. 


WITH  DISCUSSION  BY 


Messrs.  C.  A.  P.  TURNER,  T.  KENNARD  THOMSON, 
CHARLES  EVAN  FOWLER,  J.  E.  GREINER,  D.  B.  STEINMAN, 
HENRY  H.  QUIMBY,  and  GUSTAV  LINDENTHAL. 


Reprinted  from  Transactions,  Vol.  LXXXV,  p.  910  (1922). 


Date  Du 


Mar25 


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AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS 

INSTITUTED  1852 


TRANSACTIONS 

This  Society  is  not  responsible  for  any  statement  made  or  opinion  expressed 
in  its  publications. 


Paper  No.  1496 


THE  CONTINUOUS  TRUSS  BRIDGE 
OVER  THE  OHIO  RIVER  AT  SCIOTOVILLE,  OHIO, 

OF  THE 

CHESAPEAKE  AND  OHIO  NORTHERN  RAILWAY* 

By  Gustav  Lindenthal,!  M.  Am.  Soc.  C.  E. 

With  Discussion  by  Messrs.  C.  A.  P.  Turner,  T.  Kennard  Thomson,  Charles 
Evan  Fowler,  J.  E.  Greiner,  D.  B.  Steinman,  Henry  H.  Quimby,  and 
Gustav  Lindenthal. 


Synopsis 

The  peculiar  construction  of  the  Sciotoville  Bridge  has  been  the  subject  of 
frequent  inquiries,  and  the  following  detailed,  although  somewhat  belated, 
description  will  serve  as  a permanent  record,  useful  for  similar  bridge  con- 
struction elsewhere. 

The  distinguishing  features  of  the  design  are  four:  Continuous  trusses 
over  two  long  spans ; floor-beams,  acting  as  inverted  arches  and  braced  against 
tractive  forces;  erection  with  the  minimum  of  falsework  and  without  extra 
material  in  the  trusses;  and  riveted  connections  to  the  limit  of  the  largest 
rolling  mill  and  shop  facilities.  The  subject-matter  is  presented  herewith  under 
the  following  heads: 

1.  — General  Conditions  and  Selection  of  Design. 

2.  — History  and  Characteristics  of  Continuous  Truss  Bridges. 

3.  — Substructure. 

4.  — Steel  Superstructure. 

5.  — Fabrication  and  Erection  of  Steelwork. 

1. — General  Conditions  and  Selection  of  Design 

Location  and  Grades. — When  it  was  decided  by  the  Chesapeake  and  Ohio 
Northern  Railway  Company  to  bridge  the  Ohio  River  and  connect  with  the 

* Presented  at  the  meeting  of  April  5th,  1922. 
t Cons.  Engr.,  New  York  City. 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


911 


main  line  of  the  Chesapeake  and  Ohio  Railway,  on  the  Kentucky  side  (the 
southern  or  left  bank)  of  the  Ohio  River,  the  crossing  was  selected  so  as  to 
form  a direct  route  from  the  junction  to  Columbus,  Ohio,  along  the  valleys  of 
the  Little  Scioto  and  the  Scioto  Rivers,  with  exceptionally  favorable  grades 
for  the  heavy  coal  transportation  to  the  Great  Lakes  via  the  Hocking  Valley 
Railway.  Going  north,  the  grades  are  0.2%  and,  going  south,  0.3%,  and  are 
compensated  on  curves.  The  line  has  a single  track  for  the  present,  but  the 
Ohio  River  Bridge  and  the  masonry  piers  of  the  approach  viaducts  are  built  for 
two  tracks.  With  the  coal  traffic  steadily  growing,  two  tracks  for  the  entire 
line  will  be  necessary  before  long.  The  double-track  bridge  was  built  at  a period 
of  low  prices,  thus  enhancing  its  economic  advantage  in  the  development  and 
growth  of  that  important  traffic. 

River  Conditions. — At  the  site  of  the  bridge,  the  Ohio  River  has  a width 
of  about  1 600  ft.  between  embankments  and  forms  a sharp  bend.  The  river 
channel  is  near  the  inner  or  Kentucky  shore,  but  at  high-water  stages,  the 
traffic  shifts  toward  the  Ohio  shore,  along  which  also,  at  times,  considerable 
ice  and  drift  are  carried. 

The  river  channel  is  5 ft.  deep  at  low  water  and  72  ft.  deep  at  high  water. 
The  bottom  which  is  practically  bare  rock,  with  a slight  slope  from  the  Ohio 
toward  the  Kentucky  shore,  afforded  a solid  foundation  for  the  piers. 

The  requirements  of  the  War  Department  called  for  a minimum  clear 
height  under  the’  bridge  of  90  ft.  above  low  water  and  40  ft.  above  high 
water.  The  navigation  interests  demanded  large  openings,  owing  to  the  danger 
by  obstructing  piers  to  the  descending  coal  tows  some  of  which  are  150  ft. 
wide  and  700  ft.  long  and  (at  this  sharp  bend  of  the  river,  at  the  head  of  the 
shoals  of  the  Little  Scioto  River)  are  difficult  to  control,  particularly  on 
account  of  the  dense  smoke  and  fog  prevalent  in  this  locality.  On  the 
Kentucky  side,  it  was  also  necessary  to  keep  the  river  channel  open  for  naviga- 
tion during  the  erection  of  the  bridge. 

Selection  of  Design. — After  several  layouts  with  different  span  lengths,  it 
appeared  that  with  two  spans  of  750  ft.  each  in  the  clear  and  a pier  in  the 
middle  of  the  river,  the  requirements  of  the  navigation  interests  and  of  the 
War  Department  would  be  satisfied.  This  made  possible  a symmetrical  and 
sightly  structure  with  two  spans  775  ft.,  center  to  center,  of  bearings.  (Fig.  1.) 

The  rock  foundations  were  favorable  to  a continuous  truss  bridge,  which 
also  offered  the  advantage  of  erection  with  a minimum  of  falsework.  Two 
simple  truss  spans  of  775  ft.  each,  would  have  been  from  15  to  20%  more 
expensive  for  metal  and  erection. 

The  span  of  775  ft.  exceeds  in  length  the  longest  existing  simple  span 
bridge,  namely,  the  720-ft.  span  of  the  Ohio  River  Bridge,  at  Metropolis,  111., 
built  in  1917. 

It  will  thus  be  seen,  that  the  selection  of  continuous  trusses  was  primarily 
indicated  in  this  case  by  reasons  of  economy  in  metal  and  by  facilities  of 
erection. 

2. — History  and  Characteristics  of  Continuous  Truss  Bridges 

In  view  of  the  fact  that  this  bridge  has  the  longest  spans  of  the  continuous 
truss  type,  and  thus  comes  into  competition,  for  long  spans,  particularly  with 


912 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


the  simple  span  and  the  cantilever  type,  it  appears  appropriate  to  review 
briefly  its  history  and  some  of  its  characteristics  not  generally  appreciated  by 
American  bridge  engineers. 

History. — The  Britannia  Bridge  in  England,  built  by  Stephenson  in  1848, 
marks  a milestone  in  bridge  construction,  not  only  because  it  was  the  first 
important  iron  bridge  of  the  beam  type,  but  also  because  it  was  the  first  repre- 
sentative of  the  continuous  girder  type.  It  is  a tubular  plate  girder  bridge 
of  four  spans,  two  of  which  are  230  ft.  and  two  of  460  ft.  The  girders  were 
proportioned  as  simple  beams,  but  the  designer,  realizing  that  continuity 
increased  the  carrying  capacity,  regarded  this  feature  as  an  additional  safety. 
To  gain  more  information,  he  made  tests  with  a model,  and  thus  found  the 
points  of  contraflexure  of  the  elastic  line,  which  he  regarded  as  “fixed” 
and  as  dividing  the  span  into  two  “cantilevers”  and  a “central  beam”.  This 
laid  the  foundation  for  the  later  development  of  the  modern  cantilever  bridge 
by  the  introduction  of  hinges  at  the  points  of  contraflexure. 

Too  much  credit  cannot  be  given  to  that  galaxy  of  early  English  bridge 
engineers  of  nearly  one  hundred  years  ago — Stephenson,  Fairbairn,  Telford, 
Tierney  Clark — for  the  originality  and  daring  of  their  plans  and  construc- 
tions. They  did  their  own  thinking;  they  did  not  wait  for  precedents,  but 
created  them.  Theirs  was  the  genius  that  originates  as  distinguished  from 
routine  which  merely  imitates. 

The  Britannia  Bridge  was  followed  by  several  similar  bridges,  among 
which  may  be  mentioned  the  Torksey  Bridge,  built  in  1849,  over  the  Trent,  with 
two  spans  of  130  ft.,  and  the  Bryne  Bridge,  built  in  1855,  with  a central  span 
of  267  ft.  and  two  side  spans  of  141  ft.  each. 

In  the  latter  part  of  the  Nineteenth  Century,  continuous  truss  bridges  were 
extensively  built  on  the  Continent,  principally  in  France,  and  were  usually 
of  the  lattice  truss  type  with  parallel  chords,  with  from  three  to  five  spans. 
The  Fades  Viaduct  over  the  Sioule  Biver,  in  France,  built  from  1905  to  1908, 
with  a central  span  of  472  ft.,  was  the  longest  continuous  span  previous  to  the 
building  of  the  Sciotoville  Bridge. 

The  Lachine  Bridge,  built  in  1888,  by  the  late  C.  Shaler  Smith,  M.  Am.  Soc. 
C.  E.,  over  the  St.  Lawrence  Biver,  near  Montreal,  Que.,  Canada,  with  two 
side  spans  of  269  ft.,  and  two  middle  spans  of  408  ft.,  was,  for  29  years,  the 
only  continuous  bridge  in  America.  It  was  built  as  a cantilever  and  then  con- 
verted into  a continuous  truss  for  the  live  load.  It  was  replaced  in  1910  by  a 
simple  span  bridge. 

There  has  been  always  more  or  less  prejudice  against  continuous  trusses, 
because  cantilever  trusses  offer  the  alleged  more  accurate  computation  of 
stresses  on  purely  statical  principles.  No  continuous  girder  as  far  as  known 
has  ever  failed  in  the  trusses,  whereas  the  largest  and  most  discreditable  bridge 
failure  belongs  to  the  supposedly  accurate  cantilever  type. 

It  appears  now,  however,  as  if  the  continuous  truss  would  again  come  into 
its  own,  for  not  only  was  it  adopted  for  the  Sciotoville  Bridge,  but  also  for  the 
bridge  of  the  Bessemer  and  Lake  Erie  Bailroad  built  in  1918  over  the 
Allegheny  Biver  near  Pittsburgh,  Pa.,  with  spans  of  from  272  ft.  to  520  ft.,  and 
for  the  bridge  of  the  Hudson  Bay  Bailway,  across  the  Nelson  Biver,  built  in 
1918,  with  spans  of  300  ft.  and  400  ft. 


Fig.  1.— Sciotoville  Bridge  Over  the  Ohio  River. 


I 


SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 


915 


Characteristics  of  Continuous  Bridges. — The  continuous  truss  type  has 
nowhere  met  with  more  indiscriminate  and  unqualified  condemnation  than 
by  engineers  in  the  United  States,  who  have  alleged  three  principal  objections 
against  it,  none  of  which  is  novel  or  decisive: 

* 1st. — That  it  is  statically  indeterminate,  that  is,  its  reactions  and  stresses 
are  dependent  on  the  elasticity  of  its  members ; 

2d. — That  it  is  subject  to  stresses  from  unequal  settlements  of  its  supports; 
and, 

3d. — That  it  is  affected  by  temperature  changes. 

Although  these  characteristics  may  be  objectionable  in  certain  cases,  it 
can  be  readily  shown  that  they  are  entirely  unobjectionable  in  others,  and  they 
will  be  briefly  discussed. 

Static  Indeterminateness 

The  argument  that  the  stress  computations  are  complicated  can  be  readily 
dismissed.  For  preliminary  and  comparative  designs,  the  simplifying  assump- 
tion of  constant  moment  of  inertia  of  the  vertical  section  through  the  girder 
or  truss  and  the  neglect  of  the  elastic  deformation  of  the  web  members,  furnish 
sufficiently  accurate  and  quick  results.  For  the  final  design,  the  slight  addi- 
tional time  and  labor  involved  in  the  accurate  calculation  is  of  no  account 
as  continuous  bridges  will  never  be  a common  type. 

The  stress  calculation,  of  course,  is  the  more  complicated  the  greater  the 
number  of  spans,  but,  for  other  reasons,  it  is  not  advisable  to  have  more  than 
three  or  four  spans  in  a continuous  bridge. 

The  fact  that  the  stresses  are,  to  a certain  extent,  dependent  on  the  elastic 
deformation  of  the  members,  is  characteristic  of  all  statically  indeterminate 
structures,  but  in  a properly  designed  continuous  bridge  the  effect  of  even 
large  variations  in  the  elastic  behavior  is  insignificant  when  compared  with 
other  uncertain  stresses,  such  as  secondary  stresses,  etc.,  which  exist  also  in 
statically  determinate  structures. 

Variation  between  the  actual  and  the  calculated  elastic  deformation  may  be 
due,  first,  to  a difference  between  the  assumed  and  the  actual  modulus  of 
elasticity;  and,  second,  to  the  influence  of  the  details,  such  as  gussets,  splice 
and  tie-plates,  rivets,  etc.,  which  can  only  be  roughly  estimated. 

A proportional  change  in  the  modulus  of  elasticity  or  in  the  sectional  area 
of  all  members  due  to  allowance  for  details  has  no  influence  on  the  reactions 
and  stresses,  but  only  on  the  deflections  which  change  in  the  same  propor- 
tion with  the  moduli. 

The  effect  of  non-proportional  changes  is  well  illustrated  by  a comparison 
of  two  sets  of  calculations  made  for  the  Sciotoville  Bridge.  It  was  planned 
that,  during  the  various  stages  of  erection,  the  trusses  would  pass  successively 
through  static  conditions  of  a beam  on  two,  three,  four,  and  five  supports  (see 
Plate  XII).  The  calculation  of  the  reactions,  for  the  purpose  of  determining 
the  necessary  jacking  forces  at  the  temporary  supports,  and  of  the  deflections, 
for  determining  the  jacking  heights,  were  made,  first,  on  the  basis  of  the  grosfc 
area  of  the  main  section  of  the  members  without  allowance  for  details  and, 


916 


SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER 


second,  on  the  basis  of  gross  area  of  the  main  section  plus  the  area  of  a section 
equivalent  to  75%  of  the  weight  of  the  details.  This  additional  area,  due  to 
details,  varies  for  different  members  from  5 to  25%  and  averages  about  20%  of 
the  gross  area  of  the  main  section.  For  these  two  extreme  assumptions,  certain 
deflections  differ  by  25  to  60%,  whereas  the  reactions  differ  by  not  more  than 
0.2%  in  the  two-span  condition,  465  ft.-775  ft.,  10%  in  the  three-span  condition, 
155  ft.-465  ft.-775  ft.,  60%  in  the  four-span  condition,  155  ft.-155  ft.-465  ft.-775  ft., 
11%  in  the  three-span  condition,  310  ft.-465  ft.-775  ft.,  and  0.7%  in  the  final 
two-span  condition,  775  ft.-775  ft. 

The  large  differences  in  the  reactions  in  the  three  and  four-span  condi- 
tions are  due  principally  to  the  great  variation  in  the  length  of  the  spans  and  to 
the  comparatively  great  height  of  the  short  spans.  Continuous  trusses  of  great 
height  and  greatly  different  span  lengths  are,  therefore,  rightly  objectionable, 
the  more  so,  because  they  are  also  sensitive  to  settlements  of  the  supports  and 
to  temperature  changes.  During  erection,  such  a condition  is  of  no  conse- 
quence, because  the  reactions  can  be  measured  and  the  height  of  the  bearings 
promptly  adjusted  if  necessary.  Where  the  spans  are  more  nearly  equal, 
and  the  trusses  not  unusually  high  in  comparison  with  the  span  length,  the 
effect  on  the  reactions  and  stresses  from  a variation  in  the  elasticity  of  the 
trusses  is  practically  insignificant. 

As  a precaution,  and  to  obviate  any  uncertainty  of  stress  action,  from  dead 
load  at  least,  it  is  always  possible  and  advisable,  as  was  done  in  the  case  of 
the  Sciotoville  Bridge,  to  measure  certain  reactions,  and,  if  necessary,  to  adjust 
the  height  of  the  bearings  until  the  reactions  are  correct. 

In  no  case  should  the  variation  in  span  length  in  a continuous  truss  be 
so  great  that  the  live  load  on  any  span  will  cause  a reversal  of  the  dead 
load  reactions  of  the  adjoining  span.  For  all  these  reasons,  continuous  trusses 
over  several  spans  and  on  metallic  towers,  or  on  steel  arches,  should  preferably 
be  shallow  in  depth,  a rule  first  practiced  by  French  engineers. 

It  is  interesting  to  note  that  the  actual  deflections  of  the  Sciotoville  trusses, 
as  observed  in  the  field,  were  nearly  midway  between  the  values  computed 
under  the  two  previously  mentioned  assumptions;  in  other  words,  an  average 
addition  of  about  10%  to  the  gross  areas  of  the  sections,  to  allow  for  details, 
should  be  made  when  calculating  elastic  deformations. 

Effect  of  Settlements  or  Compressibility  of  Supports 

Where  considerable  settlements  of  the  foundations  are  to  be  anticipated, 
or  where  the  supports  are  high  elastic  towers,  the  continuous  type  of  bridge 
is  not  advisable,  unless  care  is  taken  to  eliminate  the  effect  of  inconstant 
levels  by  means  of  adjustable  bearings. 

The  stresses  caused  by  the  ordinary  compressibility  of  the  supports  can 
be  computed  and,  if  they  are  not  unduly  large,  can  be  neglected  or  provision 
can  be  made  in  the  sections. 

Settlements  of  the  foundations  are  less  objectionable  the  longer  the  spans, 
as  already  mentioned.  For  similar  continuous  trusses  with  equal  pro- 


SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


917 


portion  of  height  to  span  length,  the  same  settlement  of  a support  causes 
stresses  approximately  in  inverse  proportion  to  the  span  length.  As  settle- 
ments may  be  assumed  as  proportional  to  the  foundation  pressure  and  as 
the  latter  is  about  the  same  for  long  and  short  spans,  under  the  same  soil 
conditions,  it  follows  that,  in  general,  the  danger  of  excessive  stresses  due  to 
settlements  is  less  the  greater  the  span  lengths.  In  special  cases,  it  may  be 
advisable  to  design  the  permanent  details  of  the  truss  bearings  on  the  piers 
and  abutments  so  that  they  may  be  raised  or  lowered  by  hydraulic  jacks  at 
any  time,  as  needed  to  maintain  the  original  levels. 

In  the  case  of  the  Sciotoville  Bridge,  a settlement  of  2 in.  in  one  of  the  end 
piers,  if  it  was  possible,  or  a settlement  of  1 in.  in  the  middle  pier,  the  others 
remaining  undisturbed,  would  change  the  reactions  by  only  0.6  per  cent.  It  is 
evident  that  even  a considerably  greater  settlement,  which  would  seriously 
disturb  the  vertical  alignment  of  the  track,  would  not  objectionably  affect  the 
stress  condition  in  the  trusses.  When  the  Kentucky  end  of  the  bridge  was 
raised  to  its  final  position,  after  erection  had  been  completed,  difference  in  the 
jacking  force  for  the  last  3 in.  of  jacking  was  noticeable.  This  shows  that 
for  spans  of  this  length  continuous  trusses  are  unobjectionable,  even  %if  the 
foundations  do  not  rest  on  solid  rock. 

As  already  mentioned,  the  first  continuous  trusses  had  solid  webs  (Britannia 
Tunnel  Bridge)  and  on  the  Continent  small  mesh  lattice  webs.  The  sec- 
ondary stresses  in  the  web  are  of  no  importance  in  the  first  type  and,  in  the 
latter  type,  they  may  be  considered  rather  beneficial,  since  they  contribute  to 
stiffness  and  absorb  some  of  the  bending  stresses  on  the  trusses,  proven  by  the 
fact  that  the  lattice  can  bear  some  load  when  the  chords  are  cut  away,  only 
the  chord  sections  over  the  bearings  may  need  reinforcement  against  bending. 
In  some  instances,  the  continuous  small  mesh  web  girders  over  several  spans 
were  erected  on  falsework  with  a camber  of  to  of  the  entire  length 
of  bridge  and  then  let  down  on  the  pier  bearings,  to  produce  in  the 
trusses  initial  bending  stresses  opposite  those  from  live  load.  Such  was  the 
procedure  of  erection  of  the  continuous  truss  viaduct  of  five  spans  on  high 
iron  towers  over  the  Thur  at  Ossingen,  Switzerland,  in  1873.  The  writer 
was  on  the  Engineering  Staff  for  that  structure,  for  which  the  statical  com- 
putations were  considered  quite  a feat  at  that  time. 

Temperature  Effects 

Temperature  stresses  in  continuous  trusses  may  be  caused,  first,  by  the 
expansion  or  contraction  of  intermediate  supports,  particularly  high  steel 
towers,  and,  second,  by  unequal  temperature  changes  in  different  parts  of  the 
trusses  themselves  (uniform  temperature  changes  in  all  members  cause  no 
stresses). 

The  first  effect  is  similar  to  that  of  settlement  of  the  piers  and  is  greater, 
the  higher  the  intermediate  supports  and  the  shorter  the  spans.  In  some 
existing  bridges,  it  amounts  to  as  much  as  25%  of  the  stresses  from  dead 
and  live  load.  It  is,  however,  insignificant  and  negligible  in  the  case  of  long 
spans  resting  on  shallow  piers.  As  the  stresses  can  be  calculated,  it  is  easy 
to  make  the  necessary  provision  in  the  sections. 


918 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


The  second  effect  is  neglected,  as  a rule,  although  in  a case  where  the 
bottom  chords  are  protected  from  the  direct  rays  of  the  sun  by  a solid  floor, 
the  temperatures  in  the  top  and  bottom  chords  may  differ  considerably.  The 
effect  of  such  a difference  is  similar  to  that  of  a variation  in  the  elasticity 
of  the  truss  members  and  may  be  serious  in  a case  where  the  lengths  of 
spans  vary  considerably. 

In  the  case  of  the  Sciotoville  Bridge  an  average  difference  in  temperature 
of  10°  Fahr.,  between  the  top  and  bottom  chord  (the  effect  of  the  web  mem- 
bers is  insignificant),  would  change  the  end  reactions  by  only  1.5%,  which 
is  negligible. 

Summing  up,  one  arrives  at  the  well  established  conclusion  that  con- 
tinuous trusses  are  generally  unobjectionable  under  the  following  conditions: 

1st. — Where  the  lengths  of  the  spans  do  not  vary  greatly,  and  the  trusses 
are  not  unusually  high  as  compared  with  the  span  length. 

2d. — Where  the  foundations  rest  on  fairly  solid  ground,  compressibility 
of  the  soil  being  less  objectionable  the  longer  the  spans. 

3d. — Where  the  intermediate  supports  are  not  excessively  high  in  com- 
parison with  the  span  length. 

In  every  continuous  truss  there  are  a few  members,  such  as  the  chords 
near  the  points  of  contraflexure,  or  web  members  near  points  of  maximum 
moment,  which  are  most  sensitive  to  the  effects  enumerated,  because  their 
sections,  as  required  by  the  dead  and  live  load  stresses,  are  comparatively  small. 
Such  members,  as  a rule,  will  require  for  fabrication  or  erection  purposes 
a section  somewhat  in  excess  of  that  required  by  the  stresses,  to  provide  a 
certain  margin  for  possible  variation.  It  is  advisable  always  to  investigate 
such  members  and  proportion  them  so  that  they  are  strong  enough  under 
reasonably  extreme  assumptions. 

Advantages  of  Continuous  Trusses. — Against  the  disadvantages  mentioned, 
as  far  as  they  can  be  classed  as  such  in  any  given  case,  must  be  weighed  the 
advantages  which  the  continuous  type  possesses  over  the  simple  span  or  the 
cantilever. 

As  regards  economy,  it  is  not  feasible  to  make  a general  comparison 
between  the  continuous  bridge  and  the  cantilever  since  that  depends  largely 
on  the  arrangement  of  the  spans,  which  is  usually  governed  by  local  condi 
tions  and  of  necessity  must  be  different  for  the  two  types,  owing  to  their 
different  character.  In  comparison  with  a series  of  simple  spans  of  the  same 
length,  however,  the  continuous  truss  shows  a decided  economy  which  is 
greater  the  longer  the  spans  and,  up  to  a certain  limit,  greater  the  number 
of  spans.  For  long  spans,  the  saving  in  cost  may  be  as  much  as'  25  per  cent. 
For  short  spans,  the  economy  over  simple  spans  is  not  important,  but  greater 
rigidity  under  passing  loads  is  an  advantage. 

In  point  of  rigidity,  as  measured  by  the  deflections,  the  continuous  truss 
compares  favorably  with  the  simple  span  and  shows  a decided  advantage  ovot 
the  cantilever.  Its  deflections  and  amplitude  of  vibrations  are  smaller,  and 
the  elastic  line  smoother  and  devoid  of  local  kinks  such  as  occur  at  the 
hinges  of  cantilevers.  Both  rigidity  and  economy  gain  from  the  fact  that 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


919 


•l"o  Vert.RodsT^ 
aeed  equally 


2 0 apart 


DETAIL  OF  TOP  AND  COPING 


SECTION  D-D 


Vert.  Rods 
. spaced  equally 


RIVER  PIER 
16 


Fig.  2. 


920 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


truss  members  subject  to  reversion  of  stress  (tension  and  compression)  can  be 
riveted  members  proportioned  only  for  the  larger  stress. 

As  is  characteristic  of  all  statically  indeterminate  structures,  the  con- 
tinuous truss  has  the  advantage  in  that  when  a member  is  seriously  weakened, 
as  may  happen  in  the  case  of  the  derailment  of  a train  and  collision  with  the 
trusses,  the  probability  of  failure  of  the  whole  bridge  is  less  than  in  the 
case  of  the  statically  determinate  simple  span  or  a cantilever.  This  greater 
safety  is  still  more  pronounced  when  the  truss  webs  consist  of  small  mesh 
lattice. 

The  continuous  bridge  presents  no  greater  difficulties  in  erection  than  the 
cantilever,  but  it  offers  the  advantage  over  the  simple  span  in  that  it  can  be 
erected  on  the  cantilever  principle  without,  or  with  little,  additional  material. 
This  was  one  of  the  governing  factors  in  the  case  of  the  Sciotoville  Bridge. 

From  the  esthetic^  point  of  view,  the  continuous  bridge  can  well  compete 
with  the  simple  span  or.  cantilever,  if  properly  designed,  but  not  with  the 
more  artistic  arch  or  suspension  bridge. 

3. — Substructure 

Foundations. — All  the  piers  rest  on  solid  shale  rock  which  has  nearly 
vertical  stratification.  The  maximum  foundation  pressure  is  9.5  tons  per 
sq.  ft.  from  vertical  loads  only  and  12.5  tons  per  sq.  ft.,  with  longitudinal 
force  acting. 

The  foundations  presented  no  unusual  problems,  except  that  the  center 
pier  required  a very  heavy  coffer-dam  to  obviate  the  danger  of  the  coffer-dam 
being  washed  away  by  flood,  as  it  had  to  rest  on  bare  rock  bottom. 

Piers. — The  piers  are  of  concrete,  reinforced  with  steel  rods  to  pTevent 
shrinkage  and  temperature  cracks.  Both  the  up  and  down-stream  ends  of 
the  piers  are  semi-circular.  The  tops  are  marked  by  octagonally  shaped  missive 
copings  which  give  a neat  appearance  at  no  additional  expense. 

The  surfaces  are  plain,  having  been  wetted  and  rubbed  to  a smooth  finish 
with  concrete  bricks  immediately  after  the  forms  were  removed.  The  tPP 
surfaces  were  troweled  to  a smooth  finish  before  the  concrete  had  set  ani, 
after  hardening,  received  two  coats  of  cement  filler. 

The  center  pier  which  resists  the  longitudinal  force  from  the  entire  bridge 
and  carries  a vertical  load  of  16  400  tons,  is  18  by  63  ft.  under  the  copin? 
and  has  a batter  all  around  of  1 : 10.  The  shore  piers  which  carry  only  verticd 
loads  of  5 100  tons,  are  12  by  57  ft.  under  the  coping  and  are  battered  1:  2<. 

The  concrete  is  mixed  in  the  proportion  of  1 part  Lehigh  Portland  cemer-, 

2 parts  sand,  and  4 parts  gravel.  Sand  and  gravel  of  excellent  quality  weD 
obtained  from  a river  bank  a few  miles  below  the  bridge  site.  The  rein 
forcement  consists  of  1-in.  square  steel  rods,  arranged  as  shown  on  Fig.  2.  Tht 
copings  are  reinforced  longitudinally  by  20-in.  by  80-lb.  beams,  spaced  2 ft 
apart,  and  running  the  full  length  of  the  pier.  They  serve  also  to  distribut( 
the  load  from  the  bearings. 

The  pier  on  the  Ohio  shore  intersects  the  ground  surface  at  mid-height  of 
the  embankment,  about  30  ft.  above  low- water  level.  The  foundation  was 
placed  during  low  water  by  dry,  open  excavation  through  about  10  ft.  of  clay 


SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 


921 


and  8 ft.  of  loose  disintegrated  shale  rock.  This  pier  was  started  in  Novem- 
ber, 1914,  and  completed  in  March,  1915. 

The  pier  on  the  Kentucky  shore  is  near  the  bottom  of  the  embankment, 
where  the  ground  surface  is  only  about  15  ft.  above  low-water  level  and  the 
soil  is  mostly  sand.  These  conditions  made  it  desirable  to  sink  the  pier  as 
a concrete  caisson  with  a steel  cutting  edge,  a working  chamber  6 ft.  high, 
and  four  shafts  7 ft.  3 in.  in  diameter.  It  was  not  necessary,  however,  to 
resort  to  air  pressure.  All  excavation  down  to  the  solid  rock,  about  15  ft. 
below  low  water,  was  done  by  open  dredging  with  orange-peel  buckets  while 
the  caisson  was  flooded.  About  2 ft.  of  disintegrated  rock  was  removed  by 
hand,  for  which  purpose  the  caisson  was  kept  dry  by  pumping,  having  been 
carefully  sealed  with  empty  cement  bags  rolled  up  behind  the  cutting  edge. 
As  there  was  considerable  seepage  through  the  rock  bottom,  drain  sumps 
were  provided  from  which  the  water  was  pumped  during  the  concreting  of 
the  working  chamber.  These  sumps  were  finally  filled  by  forcing  cement 
grout  down  through  pipes  by  compressed  air.  The  cutting  edge  was  set  on 
June  22d,  and  the  pier  completed  on  September  14th,  1915. 

At  the  middle  or  river  pier,  the  rock  surface  is  practically  level  and  barely 
exposed  at  low  water.  The  rock  was  excavated  to  a depth  of  10  ft.  to  give 
the  pier  a firm  hold  against  dislocation  under  possible  ice  pressure.  This 
depth  also  proved  necessary  for  the  removal  of  all  disintegrated  and  seamy 
rock. 

Excavation  and  concreting  were  carried  on  within  a wooden  coffer-dam 
set  on  the  rock  bottom.  This  coffer-dam  was  16  ft.  high,  81  ft.  wide,  and  129 
ft.  long,  and  had  double  walls  10  ft.  apart.  The  space  between  the  walls  was 
filled  with  dirt  dredged  from  the  river  channel.  The  top  was  capped  with 
2-in.  planking  to  prevent  the  washing  out  of  the  fill.  Beams  8 ft.  high  were 
placed  outside  and  inside,  along  the  dam.  Although  submerged  for  four 
months  during  the  high-water  season,  the  coffer-dam  remained  intact. 

Construction  of  the  coffer-dam  was  started  in  November,  1914,  and  the 
pier  was  completed  in  May,  1915,  after  an  interruption  of  four  months  in 
the  foundation  work  during  high  water. 

The  three  piers  contain  approximately  15  000  cu.  yd.  of  concrete  and  250 
tons  of  steel  reinforcement  and  cost  $165  000,  or  $11  per  cu.  yd.  They  were 
built  on  contract  by  the  Dravo  Contracting  Company,  of  Pittsburgh,  Pa., 
with  an  average  daily  force  of  105  men. 

4. — Steel  Superstructure 

Rigidity  was  one  of  the  main  considerations  in  working  out  the  design  of 
the  steel  superstructure.  With  a few  modifications,  the  rules  of  design  were 
the  same  as  those  for  the  Hell  Gate  Arch  Bridge  and  Approaches,  and  are 
contained  in  detail,  with  explanatory  remarks,  in  the  paper  by  O.  H.  Ammann, 
M.  Am.  Soc.  C.  E.,  on  that  bridge.*  They  are,  therefore,  only  briefly  quoted 
here  insofar  as  they  apply  specifically  to  the  Sciotoville  Bridge. 

* Transactions,  Am.  Soc.  C.  E.,  Vol.  LXXXII  (1918),  p.  852. 


922 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


Loads  and  Stresses. — All  stresses  except  those  from  wind  and  lateral  forces 
were  computed  by  the  accurate  theory  of  elasticity,  considering  the  elastic 
deformation  of  all  members  after  their  section  had  been  determined.  The 
stresses  from  the  wind  and  lateral  force  were  computed  by  assuming  a constant 
moment  of  inertia  of  the  lateral  truss.  The  assumed  loads  were  as  follows: 

The  dead  load  ( D ) was  carefully  calculated  for  each  panel  point  after 
the  general  details  had  been  fully  worked  out.  A re-calculation  of  the  weight 
from  the  shop  drawings  showed  the  assumed  weight  to  be  3%  in  excess  and, 
therefore,  no  re-calculation  was  made.  The  average  dead  load  is  18.200  lb. 
per  lin.  ft.  of  bridge,  which  includes  1^400  lb.  per  lin.  ft.  assumed  for  the 
two  tracks. 

The  live  load  ( L ) on  each  track  was  as  shown  on  Fig.  3 (Cooper’s  E-60 
loading). 


§©  O © © © © o 

8 8 8 8 8 8 I 

S S 5 S 2 2 2 £ 


8 8 8 8 8 8 

© © © © © © 


© © © 


4 ##  44  44I4  44441 


U 56-0- 4^ 57-0— * 


lb. per  lin. ft. 


cb  d 

- t' 

id 

> 

[ i * 

426  000  lb. 

DIAGRAM  OF  SPECIFIED  LIVE  LOAD 

Fig.  3. 


In  cases  where  the  live  load  had  to  be  separated,  in  order  to  produce 
maximum  stress,  the  engine  load  was  placed  on  the  stretch  producing  the 
greater  portion  of  the  stress  and  a uniform  load  of  6 000  lb.  per  ft.  of  track 
on  the  stretch  contributing  the  smaller  portion. 

The  impact  (/)  was  calculated  according  to  the  writer’s  formula,  as  follows : 

T 1 200  + — 

L n 

= D + L X 600  + 4 a 

in  which, 

D = dead  load  stress,  in  pounds. 

L = live  load  stress,  in  pounds. 

a — length  of  train  behind  locomotive  tender  for  position  of  maximum 
stress,  in  feet. 

n = number  of  tracks  loaded  for  maximum  stress. 

j 

The  lateral  force  (Lat.)  from  trains  was  10%  of  the  live  load  on  one  track, 
or  Cooper’s  E-6  loading  acting  horizontally  5 ft.  above  the  rail. 

The  wind  pressure  (W)  was  800  lb.  per  lin.  ft.,  stationary  along  the  top 
chord,  700  lb.  per  lin.  ft.,  stationary  along  the  bottom  chord,  and  500  lb.  per 
lin.  ft.,  moving  7 ft.  above  the  rail. 

The  longitudinal  force  (Br.)  from  braking  or  traction  on  one  track  only 
was  60  000  lb.  on  a wheel-base  of  15  ft.  for  each  locomotive,  or  1 000  lb.  per 
lin.  ft.  of  track  for  the  whole  train. 

The  total  stress  was  as  follows:  Members  with  dead  and  live  load  stress 
were  proportioned  for  a total  stress  of  D +'  L -f-  I + Lat.  -f-  Excess,  in  which 


SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER 


923 


Excess  — (W  and  Br.)  — 20%  (D  -}-  L -f-  I -f-  Lat.).  Members  free  from 
dead  or  live  load  stress  were  proportioned  for  a total  stress  of  W + Br.  -f-  Lat. 
The  permissible  unit  stresses,  in  pounds  per  square  inch,  were  as  follows : 


Tension,  net  section  20  000 

Compression,  net  section  . . . : 20  000 

/I 

Gross  section,  20  000  — 100  / — — 20 

500  lb.,  in  which  l = the  length  and  t = the  radius  of  gyration 
of  the  whole  section. 


^ rounded  up  to  the  nearest 


For  latticed  members,  a further  deduction  of  100 


(- 
V ri 


— 20  ) was 


made,  in  which  lx  = the  length  and  rl  = the  radius  of  gyration 
of  the  unsupported  portion  of  the  section  between  lattice  con- 
nections. 


Bending  on  rolled  shapes,  girders,  and  steel  castings,  net  section.  20  000 


Bending  on  pins  30  000 

Shearing  on  webs,  shop  rivets,  and  pins 15  000 

Shearing  on  field  rivets  and  bolts 12  000 

Bearing  on  shop  rivets  25  000 

Bearing  on  field  rivets,  turning-bolts  and  pins 20  000 

Pressure  on  concrete  masonry  . 600 


The  specification  for  proportioning  compression  members  differs  somewhat 
from  that  used  in  the  Hell  Gate  Bridge.  The  specified  compression  stress  is 
applied  to  the  gross  instead  of  the  net  area  of  the  section  with  the  provision, 
however,  that  the  stress  applied  to  the  net  area  shall  not  exceed  20  000  lb.  per 

l 

sq.  in.  The  net  area  usually  governed  for  members  with  — less  than  50. 

Further,  instead  of  different  sets  of  unit  stresses  for  different  types  of 
sections  (closed  section  and  sections  with  one  or  two  open  sides),  the  same 
basic  stress  was  used  for  all  sections,  subject,  however,  to  the  previously  stated 
deduction  for  latticed  members. 

General  Proportions. — The  steel  superstructure,  as  built,  is  a double-track, 
two-span,  continuous  bridge,  with  a total  length  of  1 550.  ft.  between  centers 
of  end  piers,  or  two  equal  spans  of  775  ft.  and  two  clear  openings  of  750  ft. 
at  low-water  level. 


To  obtain  ample  lateral  rigidity,  the  width  between  centers  of  trusses  was 
made  38  ft.  9 in.,  or  one-twentieth  of  the  span  length,  although  at  first  a 
somewhat  smaller  width  was  considered  sufficient,  in  view  of  the  continuity 
of  the  lateral  truss.  The  height  at  the  middle  of  each  span  is  103  ft.  4 in. 
between  centers  of  chords^  To  fix  this  height,  the  portion  of  the  span  between 
the  end  pier  and  the  point  of  contraflexure  was  considered  as  a simple  span. 
This  portion  varies  from  three-fourths  of  the  span  length  for  uniform  load  on 
both  spans  to  seven-eighths  of  the  span  length  for  uniform  load  on  one  span 
only  and  averages  630  ft.  in  length.  The  height  of  the  truss  was  chosen 
approximately  one-sixth  of  this  length. 

The  height  over  the  center  pier  is  129  ft.  2 in.,  or  one-sixth  of  the  span 
length;  this  is  the  proper  height  for  a simple  span  of  the  same  length,  which 


924 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


has  the  same  maximum  moment  at  the  center  as  the  two-span  continuous 
bridge  over  the  middle  support. 

The  height  at  the  end  was  made  77  ft.  6 in.,  or  equal  to  a double  panel, 
in  order  to  give  the  end  posts  an  inclination  of  not  less  than  45  degrees. 
These  heights  also  secured  a pleasing  outline  for  the  top  chord.  The  web 
system  is  of  the  Warren  type,  with  subdivided  panels  of  a uniform  length  of 
38  ft.  9 in.,  which  was  found  to  be  the  most  economical. 

Truss  Members  and  Connections. — Two  preliminary  designs  of  the  trusses 
were  made,  one  with  tension  members  built  up  of  pin-connected,  16-in.  eye- 
bars  and  one  with  riveted  members  and  riveted  connections  throughout  In 
the  first  design,  all  riveted  members  had  riveted  connections  as  most  of  them 
had  to  be  designed  for  reversal  of  stress  and  no  pin  connections  were  allowed 
for  such  members.  This  design  was  unusual,  in  that  the  eye-bars  in  the 
heavier  tension  members  were  arranged  in  two  chains,  one  above  the  other, 
each  consisting  of  two  sets  of  bars  corresponding  to  the  two  webs  or  gussets 
of  the  riveted  members. 

The  principal  panel  points  were  carefully  detailed  for  both  designs,  and 
it  was  found  that  they  were  feasible,  although  requiring  unusual  connections 
and  gussets  of  the  largest  practicable  sizes. 

Bids  were  asked  on  both  designs.  The  eye-bar  design,  although  about  200 
tons  lighter,  proved  to  be  only  slightly  cheaper,  according  to  the  lowest  bid. 
The  riveted  truss  design  was  finally  adopted,  in  view  of  its  superior  rigidity, 
durability,  and  safety.  The  Sciotoville  Bridge  is,  therefore,  the  largest  truss 
bridge  with  completely  riveted  connections.  ] 

The  advantages  of  pin-connected  bridges,  namely,  cheaper  fabrication  and 
quicker  erection,  are  not  as  important  to-day  as  they  were  formerly.  With 
the  present  improved  facilities  for  punching,  drilling,  riveting,  etc.,  the  cost 
of  manufacture  and  erection  of  riveted  work  has  been  greatly  decreased,  and 
the  time  of  erection  is  a less  important  factor  than  in  the  pioneer  days  of  rapid 
railroad  construction. 

Typical  sections  of  the  truss  members  are  shown  on  the  stress  sheet  (Plate 
XI).  All  members  have  double  webs  and  all  chords  and  main  diagonals  have 
inside  and  outside  flange  angles.  Both  top  and  bottom  chords  and  the 
inclined  end  posts  have  one  solid  cover-plate  on  top.  The  bottom  flange  angles 
of  the  same  web  are  connected  by  a flange  plate  which  distributes  the  stress 
from  the  latticing  to  both  angles.  The  inclined  posts  at  the  center  pier  have 
a solid  cover,  top  and  bottom,  and  thus  form  completely  closed  boxes. 

All  the  open  sides  of  the  members  have  exceptionally  strong  latticing,  rang- 
ing from  3 by  2£-in.  by  |-in.  angles,  with  two  rivets,  to  12-in.  by  30-lb.  channels 
with  six  rivets.  Por  compression  members,  the  latticing  has  been  proportioned 
for  a transverse  shearing  force,  in  pounds,  equal  to  three  hundred  times  the 
gross  area  of  the  member,  in  square  inches.  The  members  are  stiffened 
against  distortion  by  transverse  diaphragms  about  15  ft.  apart. 

The  gusset-plates  are  in  the  plane  of  the  web-plates  of  the  members,  the 
latter  being  cut  at  the  edge  of  and  spliced  to  the  gussets  in  such  a manner 
that  the  rivets  are  in  double  shear.  The  flange  angles  extend  in  all  cases 
over  the  gussets. 


PLATE  XI. 

TRANS.  AM.  SOC.  CIV.  ENGRS. 

VOL.  LXXXV,  No.  1496. 
LINDENTHAL  ON 

SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER. 


D—  5100 
L - 3W9 
1 - 394 
W-  183 
D + I.  + 1 - S803 
Excess—  0 


’op  andBottom  chord  Members.  End  Posts  and  Diagonals 

ive  transverse  Diaphragms  about  15'apart. 

set  Pis.  at  all  Main  Panel  Points  \%  thick^ except  at  l/,8&  X.20 

set  Pis.  at  all  Secondary  Panel  Points  thick . 

set  Pis.  at  t/18&  ’thick. 

+ HI 

-8)7  Material  for  Diaphragms 

fc'Web 

4 x 4 x M Us 


D - 3032  - 2122 
L - 2305  + 269 
I - 308  + 24 

fat.  - 1295  + 1295 
W-  2559  + 2559 
Br.~  492  + 492 
D+L+I+Lat.-  6940  + 534, 
Excess  - 1663  4 2944 
Max. -8603  + 2410 


D+L+l-  693 


l6  l 

3390  •+  2373 
3102  - 718 

717  - 34 

834  - 834 

1331  “ 1331 

181  - 181 

8043  ' 787 


D+L+l  + 2943 


D+2218  +1553 

L + 2031  - 319 

1 + 463  - 10 

Lat.  + 555  - 555 

IV  + 935  - 935 

Br.  + 78-78 


Bracing 


Units  of  1000  lb. 


Panel  Points 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 

Steelwork  at  Upper  Chord  [ 

159.5 

83.7 

96.4 

84 

158.3 

77.5 

90 

78 

149.2 

0 

0 

Steelwork  at  Middle  Points 

0 

54.3 

22.6 

49.8 

0 

. 59.5 

21.2 

66 

0 

130 

0 

Steelwork  at  Lower  Chord 

196.5 

157 

200 

157.2 

196.7 

157 

187.8 

126 

148.8 

125 

146.5 

Total  Steelwork 

356 

295 

319 

291 

355 

294 

299 

270 

298 

255 

146.5 

Flooring 

27 

27 

27 

27 

27 

27 

27 

27 

27 

27 

13.5 

Total  Steelwork  and  Flooring 

383 

322 

346 

318 

382 

321 

326 

297 

325 

282 

160 

Bearings 

General  Notes: 

All  Stresses  are  given  in  Unit 
D.  denotes  Dead  Load 
L.  ••  Live  Load 

1.  “ Impact 

Lat.  “ Lateral  force 

W.  ..  Wind 

Br.  ••  Braking 

Excess  = (W+  Br.)-20*(D+L  + 


All  field  connections  of  stringei 
N shall  not  be  riveted  until  span  is 

> erected  and  self  supporting 


Computation  of  Stresses 

All  stresses  determined  by  assuming  main  trusses  and  bottom 
lateral  truss  as  continuous  over  three  supports  and  top  lateral 
trusses  as  simple  spans  between  U2  and  Z7i8 


STRESS  AND  SECTION  SHEET 


-103-4- 


PLATE  XL 

TRANS.  AM.  SOC.  CIV.  ENORS. 

VOL.  LXXXV,  No.  1496. 
LINDENTHAL  ON 

8CIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER. 


Top  Lateral  Bracing: 


SCIOTO  VILLE  BRIDGE  OYER  THE  OHIO  RIVER 


925 


I 


926  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 

The  gusset-plates  at  the  main  panel  points  are  If  in.  thick,  except  at 
panel  points,  U18  and  L20,  where  they  have  a maximum  thickness  of  3i  in. 
The  gussets  at  the  secondary  panel  points  are  II  in.  thick.  Correspondingly, 


the  webs  of  the  main  members  are  II,  If,  and  3£  in.  thick,  all  being  made 
up  of  individual  plates,  II  in.  thick.  This  uniformity  greatly  facilitated  the 
detailing  of  the  connections  and  the  avoiding  of  fillers. 


lb. 


SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


927 


As  the  full  thickness  of  the  gussets  was  not  required  for  the  full  size,  at 
some  of  the  largest  connections  the  gussets  were  split  into  two  to  four  plates, 
il  in.  thick,  of  variable  size,  in  order  to  save  weight.  The  largest  gusset-plates 
used  are  135  in.  by  If  in.  by  14  ft.  9 in.,  and  140  in.  by  II  in.  by  18  ft.  2 in. 


. All  chords  are  fully  spliced.  In  the  Ohio  span,  which  was  erected  on  false- 
work, the  splices  are  arranged  at  every  second  panel  point,  and  on  the  Ken- 
tucky side  at  every  panel  point  for  convenience  in  the  cantilever  erection. 


928 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


All  shop  and  field  rivets  of  the  main  truss  members  are  1 in.  in  diameter, 
except  at  panel  point,  U1S  and  L20,  where  they  are  l\  in.  in  diameter  and 
up  to  7|  in.  long  between  heads.  The  secondary  members  have  £-in.  shop 
and  1-in.  field  rivets.  Figs.  4,  5,  6,  7,  and  8 show  typical  connections  and 
splices. 


j 

Bracing. — There  is  a lateral  system  along  the  bottom  chords  forming  with 
the  latter  a two-span  continuous  truss.  The  laterals  pass  under  and  are  con- 
nected to  the  bottom  flange  of  the  stringers. 


Fig. 


SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


929 


930 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


* 


Fig.  11. — Steel  Casting  on  Center  Pier,  Sciotoville  Bridge. 


' £ - " 


SCIOTO  VILLE  BRIDGE  OYER  THE  OHIO  RIVER 


935 


There  is  also  a lateral  system  between  the  top  chords  from  end  to  end. 
The  portions  between  panel  points,  U2  and  Us,  are  assumed  to  act  as  simple 
spans,  transmitting  the  end  shears  at  these  points  to  the  portals  between  the 
inclined  posts.  The  laterals  and  struts  of  this  system  are  of  the  full  depth  of 
the  top  chord  (Fig.  9). 

The  portals  between  the  end  posts  and  between  the  inclined  posts  at  the 
center  pier  are  very  rigid.  The  upper  part  consists  of  rigid  single  inter- 
section braces  and  the  lower  one  of  a solid  plate-girder  arch  (Fig.  10). 

Sway-frames  between  the  other  web  members  have  been  purposely  omitted 
as  being  unnecessary  and  as  they  would  have  had  to  be  made  very  strong  to 
resist  unequal  deflections  of  the  trpsses.  Instead,  there  is  a lattice  frame  at 
every  panel  point  which  acts  as  a lateral  brace  for  the  long  web  members  and, 
at  the  same  time,  as  a strut  between  the  upper  ends  of  the  U-shaped  floor- 
beam,  the  latter  acting  as  an  inverted  arch,  as  described  later. 

The  longitudinal  struts  which  brace  the  long  verticals  at  mid-height, 
extend  over  two  panels  for  better  appearance.  They  were  also  useful  in  the 
cantilever  erection  of  the  Kentucky  span.  After  erection,  the  connection  at 
one  end  was  loosened  so  as  to  allow  it  to  slide  and  thus  prevent  the  introduc- 
tion of  indeterminate  stresses. 

Bearings. — All  bearings  are  of  cast  steel.  The  bearings  at  the  center  piei; 
are  fixed;  those  at  the  ends  are  movable.  The  longitudinal  force  from  braking 
and  traction  is  thus  transmitted  to  the  center  pier  which  carries  about  60% 
of  the  vertical  load  of  the  entire  bridge,  the  longitudinal  expansion  of  the 
bridge  being  divided  between  the  two  end  bearings. 

The  center  bearing  of  each  truss  carries  a total  vertical  load  of  16  406  000 
lb.,  inclusive  of  impact,  and  it  transmits,  further,  a longitudinal  force  of 
2 520  000  lb.  It  consists  of  the  shoe-casting  (Fig.  11),  bolted  to  the  truss,  and  a 
pedestal  made  up  of  three  individual  castings  arranged  in  two  tiers.  The 
truss  transmits  its  reactions  to  the  shoe  in  direct  bearing  by  the  gussets  which, 
for  this  purpose,  are  extended  somewhat  below  the  bottom  chord.  The  upper 
surface  of  the  shoe-casting  is  planed  slightly  convex  parallel  to  the  truss  to 
prevent  dangerous  edge  pressure,  although  the  casting  has  been  proportioned 
by  assuming  the  load  as  distributed  uniformly  over  its  full  length. 

To  concentrate  the  reactions  and  permit  the  truss  to  deflect  freely,  the 
lower  surface  of  the  shoe-casting  was  planed  to  a cylindrical  surface  with 
a radius  of  1 150  in.,  whereas  the  top  surface  of  the  pedestal  was  finished  to 
a perfect  plane.  Under  maximum  load,  the  contact  area  is  about  in. 
wide,  and  the  greatest  pressure  along  the  center  line  of  this  area  is  29  900  lb. 
per  sq.  in.,  the  average  being  23  300  lb. 

The  reactions  of  the  bottom  lateral  truss  are  transmitted  from  the  lateral 
gussets  through  diaphragms  to  a lateral  extension  of  the  shoe-casting  in  order 
to  relieve  the  gussets  of  the  main  trusses  of  transverse  bending.  The  longi- 
tudinal force  is  transmitted  from  the  main  gussets  to  vertical  lugs  of  the 
shoe-casting  by  means  of  turned  bolts  2£  in.  in  diameter.  To  prevent  hori- 
zontal motion,  the  shoe-casting  is  secured  to  the  pedestal  by  four  steel  dowels 
6 in.  in  diameter. 


Diaphragm 

Sub-Hanger 


936 


SCIOTO  VILLE  BRIDGE  OYER  THE  OHIO  RIVER 


INTERMEDIATE  FLOORBEAM 

Assumed  Wind,  Lateral  & Braking  Force 
Wind  along  Top  Chord  = 800  lb.  per  lin.ft.of  Bridge 
“ “ Bottom  Chord=700  *«  “ **  •«  “ •• 

..  on  Train  =E00  “ «*  •*  ••  « “ 

Lateral  Force  from  Train  = 10f«  of  Live  Load  (E.60)  on  one  Track 
Braking  Force  =1000  lb.  per  lin.ft.of  Bridge  on  one  Track 

or:  1000  -0Eal7c5-  =670  lb.  per  lin.ft.of  one  Truss 

Jo. 75 


Fig.  12. 


SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER 


937 


The  complete  bearing  weighs  75  tons  and  the  heaviest  individual  casting, 
21  tons.  The  end  bearings  are  much  lighter  and  are  of  the  ordinary  type  with 
a pin,  6 in.  in  diameter,  and  a nest  of  rockers,  16  in.  high.  Each  end  bearing 
weighs,  complete,  20  tons. 

Floor  System. — The  tracks  are  carried  by  four  lines  of  stringers  of  the 
usual  plate-girder  type,  which  are  framed  into  the  floor-beams. 

The  floor-beams,  however,  are  of  exceptional  design.  They  form  U-shaped 
frames  (Fig.  12),  extending  up  to  the  bottom  of  the  overhead  struts.  The 
available  height  of  the,  floor  was  too  shallow  for  an  economical  and  stiff  floor- 
beam  of  the  ordinary  type  computed  as  a simple  span  between  centers  of 
trusses.  There  was,  however,  sufficient  room  available  outside  the  train- 
clearance  line  for  wide,  deep  brackets.  By  making  the  latter  continuous  with 
the  floor-beam  proper,  it  became  admissible  to  compute  the  stresses  by  assum- 
ing the  frame  as  an  inverted  two-hinged  arch.  This  reduced  the  bending 
moments  in  the  horizontal  portion  considerably  and  effected  a substantial 
saving  in  weight.  The  overhead  strut  takes  up  the  horizontal  thrust  of  the 
inverted  arch.  The  whole  arrangement  is  contributive  to  stiffness  and  re- 
sistance to  vibration,  and  the  bridge  behaves  most  satisfactorily  in  that 
regard  under  heavy  trains. 


( one  in  each  Panel ) 

("in  Plane  of  Bottom  Flange  of  Stringers) 
FIG.  13. 


Braking  Trusses. — In  large  bridges,  traction  or  braking  trusses  are  neces- 
sary to  avoid  excessive  horizontal  bending  of  the  floor-beams  by  the  longitudinal 
forces.  In  the  Sciotoville  Bridge,  this  has  been  solved  in  a novel,  way  by 
providing  such  a truss  in  every  panel  in  the  plane  of  the  bottom  laterals 
(Fig.  13).  In  this  manner,  the  stresses  in  the  stringers  from  the  longitudinal 
force  are  reduced  to  a negligible  minimum  and  the  horizontal  bending  of  the 
floor-beams  from  that  force  and  from  the  deformation  (changes  in  length  from 
tension  and  compression)  of  the  bottom  chords,  is  avoided. 

No  expansion  joints  are  provided  in  the  floor.  This  feature  introduces 
high  longitudinal  stresses  in  the  stringers  from  the  deformation  (extension 
and  compression)  of  the  bottom  chords.  To  reduce  these  stresses  to  the 


938 


SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 


effect  of  the  live  load,  the  length  of  the  stringers  was  made  to  correspond  with 
the  length  of  the  bottom  chords  under  full  dead  load. 

The  stringer  connections  were  not  riveted  until  the  spans  had  been 
swung.  Even  so,  it  was  found  necessary  to  increase  the  number  of  rivets  in 
the  stringer  connections  above  that  required  for  the  vertical  shear,  by  about 
20%,  or  rather  the  diameter  was  increased  from  § in.  to  1 in.  To  avoid 
these  high  stresses  in  the  stringer  connections  altogether,  provision  for  an 
expansion  joint  in  each  panel  was  considered,  but  it  was  found  that  the  addi- 
tional expense  for  the  expansion  seats  for  the  stringers  would  have  been  con- 
siderable and,  moreover,  the  rigidity  of  the  floor  would  have  been  greatly 
impaired. 

An  arrangement  with  only  four  expansion  joints,  eight  panel  lengths,  or 
310  ft.,  apart,  with  a braking  truss  in  the  middle  between  two  joints,  was 
also  considered.  Its  advantage  was  a slight  saving  in  weight  of  braking 
trusses  and  comparatively  small  stresses  in  the  stringers  and  floor-beams,  both 
from  the  longitudinal  forces  and  the  deformation  of  the  bottom  chords.  In 
this  case,  however,  it  was  not  proper  to  connect  the  floor  laterals  rigidly  to 
the  stringers,  because  the  deformation  of  the  chords  would  be  transmitted 
to  the  stringers  through  the  laterals,  and  thus  severely  strain  the  latter  and 
their  connections  to  the  stringers.  To  omit  these  connections  would  increase 
the  weight  and  decrease  the  rigidity  of  the  lateral  system,  which  together 
with  the  undesirability  of  expansion  joints,  finally  decided  in  favor  of  the 
adopted  scheme. 

Deflections , Camber , and  Secondary  Stresses. — ( The  greatest  live  load  deflec- 
tions of  the  trusses  are  3 in.  from  full  load  covering  both  spans  and  4§  in.,  or 
about  1 : 2 000  of  the  span  length,  from  full  load  covering  only  one  span  (Fig. 
14).  This  is  about  the  same  as  the  deflection  of  a corresponding  simple  span 
having  a height  between  one-sixth  and  one-seventh  of  the  span  length. 

As  was  expected,  the  deflection  polygon  showed  a rather  sharp  upward 
kink  at  the  middle  support  and  indicated  high  secondary  stresses  in  the 
vicinity  of  this  support.  This  was  corroborated  by  a calculation  of  these 
stresses,  which  was  made  both  for  full  load  on  one  span  only  and  for  full  load 
on  both  spans. 

Without  provision  for  reducing  them,  the  largest  secondary  stresses  would 
be  13  300  lb.  per  sq.  in.  from  dead  load,  and  8 100  lb.  per  sq.  in.  from  live 
load,  or  a total  of  ^1  400  lb.  per  sq.  in.  in  the  bottom  chord  next  to  the  center 
bearing,  and  5 500  lb.  per  sq.  in.  from  dead  load,  and  3 300  lb.  per  sq.  in.  from 
live  load,  or  a total  of  8 800  lb.  per  sq.  in.  in  the  inclined  posts  at  the  center 
pier.  In  view  of  this,  and  on  account  of  the  rigid  truss  connections, 
it  was  considered  advisable  to  reduce  the  secondary  stresses  as  far  as  possible, 
not  only  near  the  center  support,  but  throughout  the  truss,  in  the  chords  as 
well  as  in  the  web  members.  This  was  done  by  cambering  the  trusses  for  full 
dead  load  plus  one-half  the  live  load,  covering  both  spans,  but  assembling  and 
erecting  them  so  that  the  angles  between  the  members  and  the  bevels  of  the 
joints  would  correspond  to  the  geometric  form  of  truss.  In  other  words,  under 


SCIOTO YILLE  BRIDGE  OYER  THE  OHIO  RIVER 


939 


/ 


940 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


the  load 


the  trusses  are  calculated  to  assume  their  true 


geometric 


form  and  the  members  to  become  straight  and  free  of  secondary  stresses. 

The  secondary  stresses  from  dead  load  are  thus  eliminated  and  those  from 
live  load  are  halved  or,  more  properly  expressed,  the  secondary  stresses  under 
dead  load  only  are  equal,  but  of  opposite  sign,  to  those  under  full  live  load 
covering  both  spans,  and,  in  absolute  value,  equal  to  one-half  of  those  which 
would  be  produced  by  full  live  load  if  the  angles  between  the  members  would 
correspond  to  the  cambered  form  of  truss.  The  largest  secondary  stresses, 
previously  mentioned,  are  thus  reduced  to  4 000  lb.  per  sq.  in.  in  the  bottom 
chord  and  to  1 650  lb.  per  sq.  in.  in  the  inclined  posts,  which  stresses  are 
fully  covered  by  the  margin  of  safety  of  the  direct  stresses. 

In  order  to  secure  the  greatest  safety  during  erection,  and  because  no 
reliance  was  placed  on  the  turning  of  the  ends  of  the  truss  members  as  the 
erection  proceeded,  it  was  decided  to  follow  the  erection  of  the  members  with 
the  riveting  as  soon  as  practicable  and  before  the  members  would  take  any 
appreciable  stress.  This  meant  initial  bending  of  all  truss  members  for  making 
their  connections,  which  was  accomplished  partly  by  drifting  and  partly  by 
special  jacking  operations. 

This  is  the  first  bridge,  in  which  this  method  of  reducing  secondary  stresses 
in  all  members  has  been  used.  It  is  a great  improvement  on  previous  practice, 
in  which  secondary  stresses  were  assumed  to  take  care  of  themselves,  at  the 
risk  of  overstressing  the  metal  at  the  connections. 

Steel  Weights. — The  entire  bridge  of  two  continuous  spans,  each  775  ft. 
long,  contains  13  240  tons  of  steelwork,  as  follows : 


Floor  system 

Floor  lateral  bracing 

Overhead  bracing 

Trusses  

Bearings  

Total  weight, 
in  pounds. 

3 403  200 

732  400 

1 942  400 

19  947  400 

456  200 

Weight  per  1 ft.  of 
bridge,  in  pounds. 

2 200 

475 

1250 

12  880 

295 

Total  steelwork 

26  481  600 

17  100 

The  weight  of  the  metal  in  the  two  riveted  simple  girder  spans,  each  775 
ft.  long,  of  the  usual  type,  and  for  the  same  live  load,  would  have  been  16  000 
tons,  or  20%  heavier  than  the  design  herein  described  and  as  built,  not  counting 
considerable  extra  metal  which  would  have  been  required  for  the  erection  of  the 
channel  span  by  the  cantilever  method. 

As  the  proportion  of  dead  load  to  live  load  in  these  continuous  spans  is  as 
3:2,  an  increase  of  live  load  from  E-60  to  E-75  would  increase  the  total 
stresses  from  dead  plus  live  load  on  the  average  only  10  per  cent.  That  leaves 
a large  margin  of  safety  for  the  heavier  loading  if  it  is  ever  used. 

The  truss  span  nearest  in  length  is  the  720-ft.,  double-track,  simple  girder 
span  of  the  Ohio  River  Bridge  at  Metropolis.  The  metal  weighs  8 023  500  lb., 
or  11  200  lb.  per  lin.  ft.  of  bridge,  the  light  weight  being  due  to  alloy  steel, 
eye-bars  instead  of  riveted  tension  members,  and  the  use  of  higher  unit  stresses. 


SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


941 


5. — Fabrication  and  Erection  of  Steelwork 

Quality  of  Steel. — All  parts,  except  the  rivets  and  the  cast-steel  bearings,  are 
of  open-hearth  structural  steel.  The  chemical  and  physical  requirements  for 
the  various  grades  are  as  given  in  Table  1. 

TABLE  1. 


Phosphorus,  maximum  basic 
“ “ acid. 

Sulphur,  maximum . . . 

Ultimate  streogth,  in 
pounds  per  square 

inch 

Yield  point,  minimum 

Elongation,  minimum]  £ | ft  *« 

Character  of  fracture 

Cold  bend  without  fracture 


maximum 
desired . . . 
minimum. 


Structural  steel. 

Rivet 

steel. 

Cast  steel. 

0.04 

0.04 

0.05 

0.06 

0.04 

0.08 

0.05 

0.04 

0.05 

70  000 

66  000 

58  000 

62  000 

50  000 

65  000 

35  000 

28  000 

33  000 

\ 22o/0 

28% 

20% 

Silky 

Fine  silky 

Silky  or  fine 
granular. 

180°  around  pin 
of  thickness  of 
test  piece. 

180°  flat 

90°  around  pin 
three  times 
thickness  of 
test  piece. 

Workmanship. — The  principal  requirements  for  workmanship  were  as  fol- 
lows : Punching  was  allowed  to  full  size  of  the  hole  in  the  material  up  to  £ in. 
thick ; to  Ar  in.  smaller  than  the  finished  hole  in  material  up  to  | in.  thick ; to 
in.  in  diameter  for  rivets  | in.  and  more,  in  material  in.  and  f in.  thick; 
and  to  | in.  in  diameter  for  rivets  1 in.  and  more,  in  material  ft  in.  thick. 

All  holes  punched  small  had  to  be  reamed  or  drilled  to  full  size  after  the 
assembling  of  parts.  All  other  holes  had  to  be  either  drilled  from  solid  to  full 
size  after  assembling,  or  drilled  small  and  reamed  to  full  size  after  assembling. 
As  most  of  the  material  is  it  in.  thick,  or  less,  these  specifications  provided  an 
opportunity  to  punch  holes  to  the  widest  possible  extent  and  yet  insure  the 
removal  of  all  material  possibly  injured  by  the  punching.  All  sheared  edges  of 
material  more  than  \ in.  in  thickness  had  to  be  planed  off  at  least  one-quarter 
of  the  thickness. 

To  insure  perfect  filling  of  holes,  rivets  with  a grip  less  than  four  times 
their  diameter  had  to  have,  when  cold,  a diameter  not  less  than  ^ in.  smaller 
than  the  finished  hole  where  the  holes  were  reamed  or  drilled  after  assembling, 
and  not  less  than  J in.  smaller  than  the  finished  hole  where  the  holes  were 
punched  full  size  (the  latter  occurred  generally  only  in  less  important  members). 
Rivets  of  a grip  of  four  or  more  times  the  diameter  had  to  be  tapered  to  the 
same  size  and  shape  as  those  for  the  Hell  Gate  Bridge.* 

Shop  Assembling  of  Trusses. — The  specifications  prescribed  that  the  con- 
necting parts  of  the  riveted  trusses  should  be  accurately  laid  out  and  assembled 
at  the  shop  and  that  all  rivet  holes  should  be  reamed  or  drilled  in  that  position. 

The  complete  assembling  of  the  trusses  or,  at  least,  of  a series  of  complete 
panels,  would  have  assured  the  greatest  accuracy  and  least  chance  for  errors. 
This,  however,  was  impracticable  because,  as  previously  explained,  the  angles 

* Transactions,  Am.  Soc.  C.  E.f  Vol.  LXXXII  (1918),  p.  920. 


942 


SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 


between  the  members  had  to  conform  to  the  “geometric”  form  of  the  truss, 
whereas  the  length  of  the  members  in  their  unstrained  condition  conformed 
to  the  “cambered”  form  of  truss. 

To  assemble  any  panel  or  group  of  panels  completely  would  have  required 
forcible  bending  of  the  members  and  drilling  of  the  holes  in  that  condition, 
a very  difficult  and  expensive  operation.  The  trusses,  therefore,  were  assembled 
in  sections,  as  shown  on  Fig.  15,  by  connecting  the  web  members  to  each  chord 
separately.  The  members  were  carefully  leveled  and  laid  out  with  a transit  to 
the  correct  angles,  and  the  distances  were  carefully  measured  with  a steel 
tape.  The  measurements  were  usually  made  in  the  early  morning  when  the 
temperature  was  uniform  in  all  parts. 


Connections  were  made  with  a sufficient  number  of  f-in.  tack-bolts  to  hold 
the  members  firmly  together  during  the  reaming  and  drilling  of  the  holes.  The 
holes  for  these  bolts  had  been  previously  punched  to  in.  in  diameter,  and 
all  other  holes  were  then  drilled  from  the  solid.  For  this  purpose,  all  the  holes 
in  the  top  plate  of  each  web,  in  the  position  in  which  the  members  were  laid 
for  assembling,  had  been  previously  punched  to  in.,  and  this  plate  served  as 
a template  for  drilling  the  holes.  Finally,  the  holes  which  served  for  the  tack- 
bolts,  were  reamed  to  full  size. 

The  chords  were  laid  first  to  an  exact  straight  line,  the  joints  being  brought 
to  perfect  and  forcible  contact,  and  the  reaming  and  drilling  of  the  holes  of 
the  splices  was  started  before  the  web  members  were  assembled.  The  two 
halves  of  the  main  diagonals,  having  a splice  at  the  M -points,  were  assembled 
to  each  other  in  the  shop  to  a straight  line,  then  taken  apart  and  re-assembled 
to  the  chords  in  the  assembling  yard. 

The  sub-diagonals,  hangers,  and  horizontal  struts  were  first  connected  up 
and  reamed  at  one  end,  then  shifted  slightly  for  connecting  up  and  reaming 
of  the  other  end.  While  one  end  of  the  sub-diagonals  was  being  reamed,  the 


SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


943 


other  end  was  held  in  position  by  a temporary  connection  through  a few  extra 
holes  provided  for  that  purpose,  which,  later,  were  plugged.  Connections  of 
sub-posts,  which  are  of  secondary  importance,  were  allowed  to  be  reamed  to 
an  iron  templet.  All  connections  were  match-marked  before  the  assembled 
sections  were  dismantled. 

Erection. — A detailed  description  of  the  erection  of  the  steel  superstructure 
which  offered  many  difficult  and  unprecedented  problems,  has  been  given  in  a 
series  of  articles*  by  Clyde  B.  Pyle,  kl.  Am.  Soc.  C.  E.,  Field  Engineer  for  the 
McClintic-Marshall  Company,  the  contractors  for  the  fabrication  and  erection 
of  the  steelwork.  Therefore,  only  the  general  procedure  and  the  conditions  and 
considerations  which  governed  the  method  of  erection,  will  be  mentioned  here. 

The  War  Department  required  the  maintenance,  during  erection,  of  a 
minimum  clear  opening  of  420  ft.  over  the  river  channel  on  the  Kentucky  side, 
for  navigation.  It  was  evident,  therefore,  that  this  part  of  the  Kentucky  span 
had  to  be  erected  by  the  cantilever  method. 

Ko  opening  for  navigation  was  required  under  the  Ohio  span  and  this  span 
lent  itself  better  for  falsework  erection  also  on  account  of  the  shallow  bottom. 
Even  with  that  span,  however,  great  risks  had  to  be  taken  because  of  the  danger 
of  the  falsework  being  carried  away  by  a sudden  flood,  especially  as  no  piles 
could  be  driven  on  account  of  the  rock  bottom.  To  minimize  this  danger  the 
contractor  used  narrow  falsework  towers  placed  under  the  main  panel  points 
only,  instead  of  closely  spaced  bents,  thus  leaving  openings  of  about  60  ft.  under 
the  main  portion  of  the  span  for  the  passage  of  drift  and  ice. 

The  erection  of  the  entire  Kentucky  span  as  a cantilever,  without  inter- 
mediate support,  would  have  required  heavy  additions  to  the  chords  and  some 
web  members  near  the  middle  pier.  The  plans,  therefore,  contemplated  the 
erection  of  the  four  end  panels  near  the  Kentucky  shore  on  falsework,  with  two 
panels  cantilevering  beyond,  and  the  other  fourteen  panels  by  cantilevering 
from  the  center  pier.  This  scheme  would  have  required  only  a comparatively 
small  addition  to  some  of  the  members.  The  six  panels  on  the  Kentucky  side 
would  have  been  erected  simultaneously  with  the  other  portion,  which  would 
have  saved  considerable  time.  It  would  have  required,  however,  a sepa- 
rate erection  plant  on  the  Kentucky  side,  and,  moreover,  the  connection  of 
the  two  joining  arms  would  have  presented  difficulties.  For  these  reasons, 
the  contractor  preferred  to  erect  the  entire  span  as  cantilever  from  the  center 
pier,  giving,  however,  intermediate  support  by  steel  bents  at  the  eighth  and 
fourth  panel  points  from  the  end  pier,  as  soon  as  these  points  were  reached. 
(Plate  XII.)  Thus,  the  free  cantilever  portion  was  reduced  to  twelve  panels, 
or  465  ft.  Even  so,  it  was  the  longest  cantilever  truss  ever  erected.  The  two 
falsework  towers  near  the  center  pier  on  the  Kentucky  side  were  placed  merely 
for  convenience  in  erecting  the  extremely  heavy  panels  near  that  pier  by  means 
of  the  gantry  traveler,  but  did  not  assist  in  the  cantilever  erection  of  the 
remainder  of  the  Kentucky  span. 

One  of  the  principal  features  of  the  erection  of  this  bridge  was  the  initial 
bending  of  the  members,  which  was  necessary  in  order  to  reduce  the  secondary 


* Engineering  News-Record,  January  10th  and  31st  and  December  26th,  1918. 


944 


SCIOTO YILLE  BRIDGE  OVER#THE  OHIO  RIVER 


stresses,  as  explained  previously.  These  operations,  as  well  as  the  adjustments 
in  height  of  the  trusses  at  the  end  piers  and  the  temporary  intermediate  sup- 
ports, required  elaborate  preparations  and  special  jacking  devices  (Fig.  16)  as 
fully  described  in  the  article  by  Mr.  Pyle.  The  contractors  deserve  full  credit 
for  the  careful  and  elaborate  manner  in  which  the  operations  were  prepared 
and  successfully  executed. 

In  the  main,  the  erection  procedure  was  as  follows : By  means  of  a gantry 
traveler,  the  falsework  and  on  it  the  steel  floor  system  and  delivery  tracks  were 
laid  from  the  pier  on  the  Ohio  shore  to  two  panels  beyond  the  center  pier  on 
the  Kentucky  side.  (Fig.  17.)  Then,  working  toward  the  pier  on  the  Ohio 
shore,  the  traveler  laid  the  bottom  chords  which  were  riveted  at  once  while 
lying  in  a straight  line  and  were  then  jacked  to  the  desired  camber.  In  this 
position,  the  Ohio  end  was  84  in.  lower  than  its  final  position. 

The  traveler  in  the  meantime  having  been  raised  to  its  full  height  and 
brought  back  to  the  center  pier,  the  erection  of  the  trusses  was  then  proceeded 
with,  working  toward  the  Ohio  end.  (Fig.  18.)  It  had  been  intended  originally 
to  proceed  simultaneously  with  the  cantilever  erection  of  the  Kentucky  span, 
but,  on  account  of  a shortage  of  labor  and  the  approaching  winter  and  high- 
water  season,  with  its  dangers  to  the  falsework,  all  efforts  were  concentrated 
on  the  Ohio  span  in  order  to  hasten  its  completion. 

Consequently,  the  creeper  traveler  which,  in  the  meantime,  had  been  placed 
on  top  of  the  trusses  over  the  center  pier,  had  erected  only  one  panel  on  the 
Kentucky  side  by  the- time  the  Ohio  span  was  completely  connected  up  (Fig. 
19).  The  creeper  traveler  then  proceeded  with  the  cantilever  erection  of  the 
Kentucky  span  and,  at  the  same  time,  the  timber  falsework  under  the  Ohio 
span  was  gradually  removed,  leaving  only  the  steel  columns  under  Panel 
Points  4,  8,  12,  and  16  to  support  the  trusses  (Fig.  20).  The  releasing  of  these 
columns  was  finally  accomplished  by  jacking  the  Ohio  end  of  the  span  to  its 
final  position,  when  the  Kentucky  cantilever  had  reached  about  mid-span.  The 
jacking  was  done  by  one  500-ton  and  four  200-ton  hydraulic  jacks  under  each 
truss  (Fig.  21). 

The  Kentucky  cantilever,  having  reached  the  eighth  panel  point  from  the 
end  (Fig.  20),  was  jacked  up  7|  in.  from  the  steel  bent  erected  at  that  point. 
This  procedure  was  repeated  when  the  truss  reached  the  next  bent  at  the 
fourth  panel  point  from  the  end.  The  jacking  height  at  that  point  was  1 in. 
(Fig.  22).  When  the  truss  reached  the  pier  on  the  Kentucky  shore  (Fig.  23), 
it  had  a deflection  of  164  in.  It  was  then  jacked  up  to  its  final  position  and 
placed  on  the  rocker  bearings,  whereby  the  intermediate  supports  were  released 
of  their  load.  The  final  jacking  force  agreed  so  closely  with  calculated  reac- 
tions that  no  further  adjustment  was  necessary.  Fig.  24  shows  a pair  of  the 
top  chord  members  being  lifted  simultaneously. 

The  operations  described  indicate  sufficiently  the  sensitiveness  of  the 
structure  from  variations  of  deflections  during  erection  and  the  necessity  for 
their  accurate  analysis  and  computation  in  advance  in  order  to  insure  an 
exact  fit  in  the  connections. 

The  erection  of  the  steel  work  was  started  in  June,  1916,  and  the  bridge 
was  completed  in  August,  1917.  From  the  beginning  of  the  work  on  the  coffer- 


PLATE  XII. 

TRANS.  AM.  SOC.  CIV.  ENGRS. 

VOL.  LXXXV,  No.  1496. 
LINDENTHAL  ON 

SCIOTOVI LLE  BRIDGE  OVER  THE  OHIO  RIVER. 


Ohio  Span 


20  XIII.  .Trusses  erected  to  L . K.S.,  ° ‘ 


Erection  Notes 

Creeper  moved  ahead  to  V 9 l/10K.S. 
Suspended  jacking  bridge  removed 
From  this  time  on.  the  flat  car  and 
locomotive  crane  should  not  be 
allowed  out  beyond  £,18K.S. 

Erect  steel  bent  under  Lg.K.S, 

XI  Trusses  erected  to  £.8  K.S. 

No  support  at  Ls  K.S. 


XII  Jack  up  under  Lg  K.S. with 
428  600  lb.  (429  500  lb.) 

. 4-12  200  12  200 

440  800  lb.  (441  700  lb.) 

Insert  floorbeam  at  Ls  before  jacking 

Steel  bent  under  Ls  K.S. 
erected 


No  support  at  Ln  K. 

No  jacking 

XIV  Jack  up  under Z«4  K.S. with 
423  700  1b.  (470  000  1b.) 

12  200  12  200 

435  900  lb.  (482  200  lb.) 
after  having  Inserted  floorbeam  at  Lt 


1 -Lao  L0-t 


Stage  XIV  The  actual  jacking  force  to  be  applied  should 
be  established  by  the  following  table: 

425  000  lb.  lift  of  La  — 1.02 
434  000  lb.  lift  of  Li  — 1.10 
443  000  lb.  lift  of '£,4  = 1,18 
452  000  lb.  lift  of  Li  =-1.26 
461  000  lb.  lift  of  = 1.34 
470  000  lb.  lift  of  L,  =1.42 
Whenever  the  force  applied  and  the  actual  lift 
coincide  with  the  figures  in  the  table,  we  have 
the  ideal  condition  aimed  for 


XVa  Trusses  erected  to  L0  K.S. 
No  support  at  Lo  K.S. 

No  jacking 


XVb  End  floorbeam  coupled 
to  trusses 
No  jacking 


W o c < 

«'  dd< 

+ + + • 


'■'ll  Ll 


TEMPERATURE  CORRECTIONS 
Kentucky  Side 
All  elevations  and  Jack  Loads. 
indicated  in  the  diagrams 
are  correct  at  a temperature 
of  0°  F, 

For  other  temperatures,  the 
elevations  and  Jack  Loads 
must  be  increased  by 
amounts  proportional  to 
the  following  corrections 
calculated  for  + 60°F. 

Corrections  for  + 60  F. 


XVt  :>Io  support. atXo,K.£ 
Creeper  removed 


XVII  Jack  up  under  to  K.S.  with 

1 026  600  lb.  (920  000  lb.)  when 
stress  in  Lg"Lio  should  be 
zero 


Stages 

E1..L4 

El.  L„ 

Load  L4 

Load  Lg 

XI 

xn-xm 

XIV-X.V1 

+0.68 

(+0.68') 

+0.52’ 

(+0.51) 

0 

+ 0.50* 
(+0.50*) 
+ 0.48* 
(+0.48-) 

-69  000 
(-57  000) 

+ 33  000  lb. 
(+27  000  lb.) 
+126  000  lb. 
(+104  000  lbi) 

ssss  gssssaas 

o o o'  o 

XVIII 


Jack  up  under  Lo  K.S.  with 
1 270  000  lb.  (1  357  200  lb.)  when 
thrust  on  column.  under_Lg 
should  be  zero 


XIX  Jack  up  under  Lo  K.S. with 

2 166  000  lb.  (2  167  800,1b.)  when 
thrust  on  column-under  Lg 
should  be  zero 

XX  Jack  up  under  Lo, K.S. with 
2 261  000  lb.  ( 2 265  000  lb.) 


El, + 584.33^ 


9 581  800  lb  ^ 
(9  548  8001b) 


at  L4 

Deflection  atLs 

3.10) 

15.12) 

-13.03  (-15.82) 
-37.22  (-45.03) 
"66.27  (-80.20) 

4.72) 
3.69) 
2.51  ) 

2.63  (3.19) 
2.08  (2.51  ) 
1.52  (1.84) 

13 

0.0193 

Lo 

2 232  150  lb. 

(2  248  600  lb) 

DIAGRAMS  SHOWING  PRINCIPAL  ERECTION  STAGES. 
DEFLECTIONS  AND  JACKING  OPERATIONS 

'NOTES:- All  Reactions  and  Jacking  Loads  are  given  in  Pounds  for  one  Truss. 
All  Deflections  are  given  in  inches. 

Figures  in  parentheses  are  computed  on  the  basis  of  no  allowance 
made  for  details  as  affecting  the  cross-sections  of  the  members. 

AH  other  figures  are  computed  on  the  basis  of  an  addition  to  the  cross 
sections  eauivalent  to  76&of  the  weight  of  the  details  of  the  members. 
Figures  of  elevations  denote  the  height  above  or  below  a horizontal 
line  through  the  Lj > point.  (El.  Base  of  Rail  + 690.08.) 

O.  S.  denotes  Ohio  Span.  K.  S.  denotes  Kentucky  Span 
Compare  Me  Clintic  Marshall  Co.’s  Drawings:  D\  ,Z?2  ,D%  & £>* 


PLATE  XII. 

TRAN8.  AM.  80C.  CIV.  ENQR8. 

VOL.  LXXXV,  No.  1496. 
LINDENTHAL  ON 

SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER. 


Kentucky  Span 

a. 


XI  Trasses  erected  from  L o O.S.  I 
L,i f,  U , K S. 

Floor  coupled  to  Lg  K.S. 
Creeper  at  U9  U\q 
Supports  at  L0  O.S.:  L*, 


XU  Supports  at  L0  0. 9.;  Lj^Lg  K.S. 


XIII  Trusses  erected  from  La  O.S.  to 
L,Afg£75K.S. 

Floor  coupled  to  L 5 K.S. 

Creeper  at  D*  £/g  K.S. 

Supports  at  L0  O.9.;  L^.-Lg  K.S. 


'«  *■»  - 


Reactions  8 188  000  lb. 


1.24  Jj== 

44*7800  lb. 
(441  700  lb.) 


Erection  Notes 

Creeper  moved  ahead  to  U9  C/WK  S. 
Susoonded  Jacking  bridge  rem< 

From  this  time  on  the  flat  car 
loeomotivo  crano  should  not  b« 
allowed  out  beyond  L,eK  S 
Erect  steel  bent  undor  L%  K.S, 


XII  Jack  up  under  Lg  K.S. with 
428  600  lb.  (429  500  lb.) 

♦ 12  200  12  200 
440  800  lb.  (441  700  lb.) 

Insort  floorbeam  at  Lg  before  jacking 


c 

1 ( 2 000  oc 


XIV  Supports  at  L0O.S.;L2n;L4&Lg  K.S.  $5 


.TWf136 


(20000001$,,. 


XIII.  Trusses  erected  to  L ♦ K.S. 
No  support  nt  L«  K.S. 

No  jacking 

XIV  Jack  up  undorL4  K.S.wIth 
428  700  1b.  (470  0001b.) 

12  200  12  200 


XVa  Trasses  erected  from  Lo  O.S.  to 
Lo  K.S. 

Floor  coupled  to  L\  K.S. 
Creeper  at  U2  17  a K.S. 

Supports  at  Lo  O.S.;  L20; 

L«&Xg  K.S. 


XV6  Floor  coupled  toLoK.S. 
Supports  at  L0  O.S.;  L201 
L4  & Lg  K.8. 


XVI  Trusses  orectod  from  L0  O.S,  t 
Lo  K.S. 

Floor  coupled  toLo  K.S. 
Creeper  removed 
Supports  at  Lo  O.S.;  Ljo5 
L«&LgK.S. 


M 

Stage  XIV  The  actual  Jacking  force  to  be  applied  should 
be  established  by  the  following  table; 

426  000  lb.  lift  of  H- 
484  000  lb.  lift  of  L,  ■= 

448  000  lb.  lift  of  Lo 
4bt  000  lb.  lift  of  Lo 
461  000  lb.  lift  of  L.: 

470  000  lb.  lift  of  L 4 • 

Whenever  the  force  applied  and  tho  actual  lift 
coincide  with  tho  figures  in  tho  table,  wc  have 
tho  Ideal  condition  aimed  for 


XVa  Trusses  erected  to  L0  K.S. 
No  support  atL0  K.S. 

No  jacking 


U,  U,  o ___ 

- 7\ 

> 

\M 

i: 

_ 

K 

/N 

7' 

:> 

< 

. 

XVII 


Supports  at  L0  O.S.;  LK;L9  K.S.  7 


TEMPERATURE  CORRECTIONS 
Kentucky  Side 
Ail  elevntiona  and  Jack  Loads. 
Indicatod  in  the  diagrams 
aro  correct  at  a temperature 
of  0°  F. 

For  other  temperatures,  the 
olovations  and  Jack  Loads 
must  be  increased  by 
amounts  proportional  to 
tho  following  corrections 
calculated  for4-60°F. 

Corrections  for  4-  60  F\ 


'’^<£0*8  SSSS 


Reactions 
from  dead 
flooring  a 


Lo  K.S. .Ljn:L0  O.S. 


? JX. 


=SSS3Sg|S39sS 


r ^ 

it 

2 278  7.0  lb  , 

(2  206  *00  n>) 


L 10  -Ln  L 1,  L 16  L 


EI.L4 

El.  Lg 

Load  L4 

UtiL, 

xc 

xn-xiri 

XIV-XVI 

4-0.68" 
(4-0.08) 
4-0.62 1 
(f  0.61) 

4-0.60’ 
(4  0.50') 
+ 0.46; 
(+0.48) 

-69  000 
(-67  000) 

4-83  000  lb. 
(4-27  OIK)  lb.) 
4-126  000  lb. 
(4-104  000  lb.) 

s*ss  S 1 5 5 3 3 ’ 

d d d d dd  d d - - - 

+ 4 + + ♦+♦♦  + £: 

!?»«!!* 

XVII  J.ck  up  undor  Lo  K.S.wIth 

1 026  600  lb.  (920  000  lb.)  when 
Btr.B.  In  t/n'E/io  should  bo 


Jock  up  undorLo  K.S.wIth 
I 270  000  lb.  (I  867  200  lb.)  when 
thrust  on  column. underXn 
should  b.  zoro 


XIX  Jock  up  undorLo  K.S.wIth 

2 166  000  lb.  (2  157  800.1b.)  when 
thrust  on  columo'under  Lg 
should  b.  zero 


El.-t-684.33i, 


DEFLECTION  CONSTANTS  (Ky.Side) 


Deflection  atLo 

Deflection  alLt 

Deflection  at  Ls 

Bridge  erected  to  Lg  . Traveler  at  U9  (Jn 

Bridge  erected  to  L«  . Traveler  at  f/g  £76 
Bridge  erected  to  Lo  . Traveler  at  U?  £7 3 

-121.88  (-148.06) 

-61.99(-63.10) 
-94.93  (-115.12) 

-18.03  (-16.82) 
-37.22  (-46.03 ) 
-60.27  (-80.20) 

100  000  lb’,  at  L°,  ~~ 

100  000  lb.  at  Lh 

6.17  (6.27) 

3.90  ( 4.72) 
2.63  ( 3.19) 

3.90  (4.72) 
3.06  (3.69) 
2.08  (2.51) 

2.63  (8.19) 
2.08  (2.61) 
I.S2  (1.84) 

Column  Compression  for  a load  of  100  000  lb. 

0 

0 0193 

0.0193 

I’ll  Ln  L io  L,  i,  L.  Lt 


DIAGRAMS  SHOWING  PRINCIPAL  ERECTION  STAGES. 
DEFLECTIONS  AND  JACKING  OPERATIONS 

‘NOTES’- All  Reactions  and  Jacking  Loads  are  given  in  Pounds  for  one  Truss. 
All  Deflections  are  given  in  inches.  ..  .... 

Figures  in  parentheses  are  computed  on  the  basis  of  no  allowance 
made  for  details  as  affecting  the  cross-sections  of  the  members. 

All  other  figures  are  computed  on  the  basis  of  an  addition  to  the  cross 
sections  equivalent  to  76%of  the  weight  of  the  dotaiis  of  the  members. 
Figures  of  elevations  denoto  the  height  above  or  below  a horizontal 
line  through  the  Ljn  point.  (El.  Base  of  Rail  4 6‘J0.08.) 

O.  S.  denotes  Ohio  §pan.  K.  S.  denotes  Kentucky  Span 
Compare  Me  Clintic  Marshall  Co.'s  Drawings:  D\  ,D2  ,D^  & D4 


Fig.  16. — Special  Jacking  Apparatus,  Sciotoville  Bridge. 


Fig.  17. — Erection  of  Falsework  and  Laying  of  Steel  Floor  System  and  Tracks  by 
Gantry  Traveler,  Sciotoville  Bridge. 


Fig.  19. — Erection  of  Ohio  Span  Completed,  Sciotoville  Bridge. 


Pig.  20. — Cantilever  Erection,  Kentucky  Span,  and  Falsework  Under  Ohio  Span 
Removed,  Sciotoville  Bridge. 


Fig.  21. — Adjustment  of  Kentucky  Span,  Sciotoville  Bridge,  by  Hydraulic  Jacks. 


Fig.  23. — Kentucky  Span,  Sciotoville  Bridge  : Temporary  Supports  Ready  for 

Dismantling. 


FIg.  24. — Pair  of  Top  Chord  Members,  Sciotoville  Bridge,  Being  Lifted 

Simultaneously. 


•'  4 n , • 


; .vijir/'; i 2 tKK  s«  jn 


SCIOTO YILLE  BRIDGE  OYER  THE  OHIO  RIVER 


953 


dam  for  the  middle  pier  in  November,  1914,  to  the  completion  of  the  super- 
structure in  August,  1917,  in  all  2 years  and  10  months  were  required  for  the 
work  which,  under  normal  labor  conditions,  would  have  taken  less  than  2 years. 

The  writer  was  assisted  in  this  unusual  work,  bristling  with  new  problems 
and  difficulties,  by  O.  H.  Ammann,  M.  Am.  Soc.  C.  E.,  as  Principal  Assistant 
Engineer  in  general  charge;  D.  B.  Steinman,  M.  Am.  Soc.  C.  E.,  on  computa- 
tions of  superstructure;  and  W.  A.  Cuenot  in  the  drafting  and  checking  of 
detail  plans.  K.  T.  Kobinson,  Assoc.  M.  Am.  Soc.  C.  E.,  acted  as  Resident 
Engineer,  and  R.  E.  McGough  as  Chief  Inspector  of  Steelwork  at  the  shops. 

The  foundations  and  masonry  were  satisfactorily  executed  by  the  Dravo 
Contracting  Company  of  Pittsburgh.  The  steel  superstructure  was  fabricated 
and  erected  by  the  McClintic-Marshall  Company  of  Pittsburgh,  under  its 
Chief  Engineer,  the  late  Paul  L.  Wolfel,  M.  Am.  Soc.  C.  E.  The  erection  was 
in  charge  of  E.  A.  Gibbs,  Assoc.  M.  Am.  Soc.  C.  E.,  General  Manager  for 
McClintic-Marshall  Company,  with  Mr.  Clyde  B.  Pyle  as  his  Field  Engineer. 

The  writer  desires  here  especially  to  acknowledge  the  conscientious  and 
painstaking  labor  of  his  assistants  and  the  helpful  experience  of  the  con- 
tractors, who  combined  in  the  successful  completion  of  the  work. 


954  DISCUSSION  ON  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 

DISCUSSION 


C.  A.  P.  Turner;*  M.  Am.  Soc.  O.  E.  (by  letter). — This  paper  on  the 
Sciotoville  Bridge,  coming  as  it  does  from  an  engineer  who  has  earned  his 
place  in  the  front  rank  of  the  Profession  by  the  design,  and  execution  of 
one  of  the  finest  examples  of  long-span  bridge  construction — the  Hell  Gate 
Arch  Bridge — will  be  received  and  read  with  unusual  interest.  The  structure 
described  is  pleasing  in  appearance,  satisfactory  from  the  standpoint  of  rigidity 
and  safety,  and  was  erected  in  a creditable  manner  without  mishap. 

The  span  is  somewhat  in  excess  of  those  common  in  simple  bridge  truss 
design;  but  the  fact  that  it  is  a double-track  structure,  and  is  wider  and  of 
correspondingly  greater  weight  than  a single-track  railway  bridge  or  the 
ordinary  highway  bridge,  should  extend  the  economic  span  length  for  the 
simple  truss  up  to  850  ft.  at  least. 

As  an  advocate  of  the  continuous  bridge,  Mr.  Lindenthal  does  not  limit 
its  application  to  long  spans  in  place  of  the  cantilever,  but  contends  that  it 
is  economical  for  spans  customarily  regarded  as  solely  within  the  province  of 
the  simple  truss  span.  In  assuming  this  position,  he  has  raised  fundamental 
questions  regarding  the  underlying  considerations  affecting  the  economy  of 
truss  design. 

The  disadvantages  of  the  continuous  structure  have  been  reasonably  and 
fairly  treated  in  the  paper.  They  should  not  prevent  the  adoption  of  the  type, 
providing  economy  results.  However,  if  the  economy  claimed  by  the  advocates 
of  the  continuous  truss  is  unsubstantiated  by  the  application  of  mechanical 
laws  governing  economic  proportions  and  form,  then  the  field  of  the  type  is 
limited  to  long  spans  which,  designed  with  economic  depth  for  vertical  loads 
as  simple  spans,  would  be  top-heavy  under  the  overturning  moment  of  wind 
pressure. 

In  the  now  classic  controversy  between  Mansfield  Merriman,  M.  Am.  Soc. 
C.  E.,  and  Charles  Bender,  on  the  relative  merits  of  continuous  versus  simple 
span  bridge  structures,  Merriman  as  a strong  point  predicated  the  economy  of 
the  continuous  truss  as  against  the  simple  truss  on  the  known  economy  of  con- 
tinuous beams  of  uniform  section.  Bender  claimed  that  he  could  design  a 
series  of  simple  trusses,  which  would  meet  the  requirements  of  a given  specifica- 
tion with  less  metal  than  his  opponent  could  design  a continuous  bridge 
covering  several  spans. 

It  would  seem  that  the  analogy  between  the  economical  relations  of  the 
continuous  beam  to  the  simply  supported  beam  is  inapplicable  to  the  rela- 
tions of  the  simple  versus  the  continuous  truss  frame,  because  the  web  is  of  con- 
stant section  in  the  beam,  whereas  in  the  truss  it  is  proportioned  to  meet  the 
requirements  only  of  the  variation  of  shear  along  the  length  of  the  span. 

Again,  although  the  claimed  ability  of  Bender  to  design  simple  trusses 
of  less  weight  than  the  continuous  frame  proposed  by  Merriman,  might  decide 
the  question  of  ability  of  the  contestants,  it  wojuld  not  necessarily  settle  or 
explain  the  principle  at  issue. 


* Cons.  Engr.,  Minneapolis,  Minn. 


DISCUSSION  ON  SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


955 


As  in  the  case  with  the  beam,  the  truss  frame  is  called  on  to  support  the 
moment  tending  to  elongate  the  bottom  chord  and  shorten  the  top  chord 
horizontally,  and  the  shear  or  cross-breaking  vertical  force.  The  total  weight 
of  the  frame  is  the  sum  of  the  weights  of  the  members  designed  to  support 
these  different  forces  added  to  the  weight  of  the  floor  system  and  lateral 
bracing. 

Simple  Bridges  vs.  Continuous  Bridges — Parallel  Chords. — With  parallel 
chords,  the  cross-section  and  the  weight  of  the  chord  decrease  as  the  depth  of 
the  frame  increases,  and,  conversely,  the  weight  of  the  web  increases  as  the 
depth  increases.  Therefore,  in  such  a frame,  the  economic  weight  approaches 
a minimum  when  the  weight  of  the  web  equals  the  weight  of  the  chords,  and 
this  relation  holds  true  whether  the  frame  is  continuous  or  simple. 

Economic  Depth  Greater  for  Simple  Span. — Continuity  renders  the  live 
load  shears  resisted  by  the  webbing  somewhat  greater  than  those  in  the  simple 
span.  Therefore,  the  web  of  the  continuous  span  would  be  heavier  than  that 
for  the  simple  span,  but  the  maximum  moments  are  smaller  for  the  continuous 
span.  If  it  is  a through  span  with  inclined  end  posts,  the  chord  length  is 
shorter  in  the  simple  span  than  in  the  continuous  span  and  if,  for  this  rea- 
son, the  chords  were  assumed  to  be  equal  in  weight  with  trusses  of  the  same 
depth,  then,  because  of  the  difference  in  the  webbing,  the  economic  depth  of 
the  simple  span  would  of  necessity  be  greater.  Parallel  chord  bridges,  how- 
ever, are  not  economical  for  even  moderately  long  spans  and,  for  these  trusses 
of  variable  depth,  there  is  a more  radical  difference  in  the  relative  economic 
depth  than  for  the  case  of  parallel  chord  bridges  of  the  two  respective  types. 

Economic  Depth — Non-Parallel  Chords. — Simple  Spans. — The  reverse  law 
of  summation  of  shears  and  moments  is  most  favorable  to  the  simple  span. 
Thus,  shear  increases  from  mid-span  to  the  support,  and  applied  moment  in- 
creases from  the  support  to  mid-span.  Accordingly,  the  simple  span  truss 
may  be  made  deep  at  the  center  and  of  small  depth  at  the  end.  With  the 
greater  depth  at  the  center  where  the  shear  is  the  least,  the  web  members, 
although  long,  are  light.  With  decreaieed  depth  toward  the  support,  the  heavy 
web  members  are  short,  so  that  by  this  arrangement  the  weight  of  the  web 
becomes  greatly  reduced  over  the  case  of  parallel  chords.  Moreover,  because 
of  the  inclination  of  the  chord,  the  inclined  chord  functions  in  a dual  capacity, 
resisting  both  shear  and  moment,  still  further  reducing  the  weight  of  the 
web  which,  with  the  parallel  chords,  was  one-half  the  total  truss  weight. 

Contrast  this  reverse  law  of  summation,  so  helpful  to  the  economy  of  the 
simple  span,  with  the  conditions  which  are  unfavorable  in  the  continuous 
span.  The  moment  is  greatest  numerically  over  the  support  where  the  shear 
is  greatest  and  to  obtain  depth  to  resist  this  moment,  heavy  web  members 
become  long  in  place  of  the  correspondingly  short  members  of  the  simple  span 
resisting  the  same  shear.  The  economic  depth  for  the  simple  span  thus  becomes 
from  20  to  30%  greater  than  for  the  continuous  truss  for  more  moderate  spans 
with  reduction,  in  view  of  overturning  moment  of  wind  for  the  longer  spans. 

As,  with  economic  height,  the  web  of  the  simple  span  would  reduce  to 
about  one-third  the  weight  of  the  continuous  type,  and  the  chord  lengths 
would  be  less,  the  conclusion  appears  inevitable  that  instead  of  the  economy 


956 


DISCUSSION  ON  SCIOTOVILLE  BRIDGE  OYER  THE  OHIO  RIVER 


claimed  for  the  continuous  frame,  it  is  generally  lacking  in  economy  to  the 
extent  of  30  to  35%,  as  compared  with  the  simple  truss  frame  for  moderate 
spans.  The  question  of  the  economic  frame  or  truss  is  only  a part  of  the 
problem  of  economic  bridge  design.  The  lowest  total  cost  is  the  object  that 
the  progressive  engineer  strives  to  attain,  but  rarely  achieves.  As  he  ap- 
proaches it  from  a consideration  of  the  minimum  truss  weight,  other  factors 
appear,  which  are  antagonistic  to  the  triangulation  he  has  fixed  on,  for  truss 
economy.  It  may  be  said  that  although  the  economic  theory  of  design  may 
appear  to  be  very  simple  in  theoretical  works  on  bridges,  in  practice,  it  is 
otherwise. 

The  truss  triangulation  which  gives  apparently  the  least  weight  for  the 
truss,  commonly  gives  difficulty  in  obtaining  desirable  panel  lengths  for  the 
floor  system;  the  stringers  are  either  too  long  or  too  short;  there  is  always 
something  that  does  not  fit,  and  the  resulting  solution  is  a series  of  compromises 
to  approximate  the  desired  end.  Again,  in  the  longer  span  bridge,  if  the  depth 
is  economic  for  vertical  loading,  it  will  be  ill  proportioned  to  resist  the  over- 
turning moment  of  severe  storms,  unless  the  floor  is  wide  and  the  work  heavy. 

Viewing  the  Sciotoville  Bridge  as  a continuous  truss  span,  the  writer 
believes  Mr.  Lindenthal  has  approached  closely  to  the  proper  economic  depth. 
His  view  that  the  steel  weight  is  20%  less  than  that  of  a properly  designed 
simple  span  is  mistaken,  and  the  writer  would  substantiate  his  view  by  the 
submission  of  Fig.  25,  which  shows  the  proportions  of  the  Sciotoville  Bridge, 
together  with  a suggested  form  of  simple  truss  span  which,  approximate 
computation  indicates,  would  be  lighter  than  the  continuous  design  by  the 
margin  noted.  The  moment  over  the  support  and  the  moment  at  the  center 
of  the  continuous  and  simple  span  design  would  be  equal.  As  the  simple 
span  is  about  10%  deeper,  the  maximum  cross-section  of  the  chord  will  be 
nine-tenths  as  great  in  the  simple  span.  As  the  simple  span  design  is  such 
that  advantage  is  taken  of  the  reverse  summation  of  shear  and  moment  to 
an  extent  impossible  in  the  continuous  span  and,  because  of  the  greater  in- 
clination of  the  chord  members  in  the  latter,  the  web  proper  would  be  about 
one-third  of  the  weight  of  the  web  of  the  continuous  span  and,  again,  the 
total  weight  of  the  chords  would  be  less,  because  of  the  shorter  length,  and 
it  would  appear  that,  as  far  as  the  truss  frame  is  concerned,  there  should  be 
a difference  of  at  least  35%  in  favor  of  the  simple  span  as  against  the  con- 
tinuous frame. 

Consider  the  floor  system:  As  the  panel  length  is  shorter,  the  stringer 
moments  will  be  approximately  six-tenths  as  great  for  the  simple  span,  and  the 
dead  load  moment  would  be  one-half  as  great.  The  floor-beams  would  be 
increased  in  number,  but  reduced  in  cross-section.  The  number  of  main 
joints  in  the  truss  would  be  few,  with  longer  members  to  handle,  thereby 
reducing  details.  Wide  variation  in  the  make-up  of  the  top  chord  and  end 
post  of  the  continuous  type  would  be  avoided,  and  simplification  of  details 
would  result  from  greater  uniformity  of  sections.  The  breaking  truss  to 
stiffen  the  floor-beams  laterally  would  be  eliminated  automatically  and  the 
lateral  system  reduced  in  weight  by  connecting  the  laterals  at  the  center  of 
alternate  floor-beams.  Lateral  stiffness  would  be  secured  by  full  triangulated 


DISCUSSION-  OH  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 


957 


958 


DISCUSSION  ON  SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


bracing  on  a smaller  number  of  planes  than  the  portal  bracing  used,  with  a 
corresponding  reduction  in  weight.  A batter  of  the  trusses  of  5 ft.  from  the 
vertical  in  the  total  height  would  add  to  the  lateral  rigidity  and  permit  some 
reduction  of  section  otherwise  required  for  top  lateral  and  chord  bracing. 
The  number  of  members  which -perform  no  work  as  truss  members,  other  than 
supporting  the  dead  weight  of  the  chords,  would  be  greatly  reduced  in  the 
suggested  simple  span. 

The  simple  truss  design  suggested  might  come  somewhat  outside  the  pale 
of  precedent  which  Mr.  Lindenthal  commends  in  the  work  of  the  early  builder, 
but,  because  it  is  practical,'  it  should  not  be  considered  a criticism  of  the 
serviceable  and  excellent  structure  described  in  this  interesting  paper.  Ap- 
proach to  the  goal  of  ultimate  economy,  for  which  all  engineers  are  work- 
ing and  may  never  expect  to  reach,  must  create  precedent. 

Erection. — In  order  not  to  exceed  the  cost  of  erection  of  the  continuous 
bridge,  the  method  of  erection  of  the  simple  span  would  likewise  need  to 
follow  somewhat  unprecedented  lines.  The  fact  that  the  river  bottom  is  of 
sound  rock  would  make  the  problem  much  simpler  than  if  dealing  with  the 
Missouri  River  where  there  is  from  50  to  60  ft.  of  shifting  silt.  Leaving  a 
wide  channel  under  one  span,  as  was  done  in  the  erection  of  the  Sciotoville 
Bridge,  would  necessitate  the  cantilever  erection  of  three  main  panels  of  one 
span,  which  would  not  appear  to  present  any  especial  difficulty. 

Although  opinion  may  differ  on  the  relative  cost  of  erection  of  the  two 
types,  of  the  quantity  of  steel  required  for  the  same  specified  working  stresses, 
any  difference  of  opinion  is  readily  solved  by  working  out  the  designs  and 
calculating  the  weights,  if  the  approximate  solution  by  the  application  of 
mechanical  principles  is  considered  open  to  question. 

Many  American  engineers  have  made  as  conscientious  an  effort  as  Mr. 
Lindenthal  to  design  continuous  truss  bridges  economically,  impelled  thereto 
by  the  mistaken  assumption  of  some  proportionate  economy  comparable  to  the 
divergence  of  the  moment  areas  of  the  two  respective  types,  only  to  realize, 
more  or  less,  the  heavy  handicap  imposed  by  the  reverse  law  of  summation  of 
shear  and  moment  favorable  to  the  simple  span  and  unfavorable  to  the  con- 
tinuous truss.  In  the  comparison  of  the  cantilever  and  continuous  type,  the 
moment  areas  approach  identity  for  comparable  depth  and  section  over  and 
between  supports,  and,  therefore,  it  would  appear  that  the  discredit  Mr. 
Lindenthal  would  cast  on  the  cantilever  truss  should  be  focused  rather  on  a 
degenerate  section  typified  by  all  web  and  no  flange,  toward  which  the  make-up 
of  the  compression  members  in  many  designs  has  carelessly  approached  and, 
in  the  unfortunate  instance  of  the  cantilever,  the  ultimate  danger  line  had  been 
passed. 

In  the  foregoing  discussion,  the  consideration  of  the  web  as  that  part  of 
the  truss  between  the  external  chords  is  a departure  from  the  comparison  of 
the  equality  of  the  web  and  chords*  in  the  parallel  truss  bridge.  It  would 
seem,  therefore,  that  the  inclined  chord  or  end  post  might  be  apportioned  as 
web  or  chord  as  the  sine  and  cosine,  respectively,  of  its  angle  of  inclination.- 
On  this  basis,  a fair  mathematical  apportionment  might  be  realized,  an  equal- 
ization from  which  reasonably  satisfactory  conclusions  could  be  drawn  as  to 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


959 


the  economic  depth  in  the  types  under  consideration.  Because  there  is  very 
little  inclination  in  the  chords  of  the  continuous  bridge,  the  apportionment 
suggested  immediately  indicates  greater  economy,  as  the  hypothenuse  of  the 
triangle  is  less  than  the  length  of  the  other  two  sides,  the  sine  and  cosine 
of  the  angle  of  inclination,  another  viewpoint  is  had,  from  which  comparisons 
and  conclusions  may  logically  be  drawn. 

The  theory  of  economic  truss  proportions  is  too  complicated  to  be  embodied 
in  simple  mathematical  form.  The  suggestion  of  Mr.  Bender,  that  the  best 
method  of  comparison  of  any  two  designs  of  similar  types,  without  going  into 
details  too  completely,  was  by  multiplying  the  length  of  the  members  by  the 
maximum  stress  thereon,  and  the  sum  total  of  the  products  should  be  a 
minimum  for  the  economic  frame,  appears  in  the  light  of  a good  approxima- 
tion, providing  the  uniformity  of  sections  and  such  lack  of  wide  variation 
as  occur  in  the  change  of  sign  and  intensity  of  the  chord  stress  presented  by 
the  continuous  truss,  in  comparison  with  the  constant  kind  of  stress  and 
relative  uniformity  presented  by  the  arched  chord  simple  span.  The  wide 
variation  in  the  stress  of  the  chords  of  the  Sciotoville  Bridge  undoubtedly 
accounts  for  the  uneconomical  thickness  of  the  webs  of  the  sections,  their 
lack  of  breadth  in  proportion  to  the  height  of  the  truss,  and  that  apparently 
unavoidable  compromise  in  the  make-up  from  which  the  designer  would  be 
free  in  treating  the  simple  truss  span. 

If  engineers  are  to  consider  the  Sciotoville  example  as  a riveted  trus3  of 
unprecedented  dimensions,  they  should  not  forget  the  old  Forth  Bridge  with 
clear  spans  of  1 700  ft.,  and  its  riveted  construction  throughout.  Riveted 
construction  in  simple  span  design  has  the  inherent  advantage  that  rolled 
shapes  which  make  up  the  members  can  be  secured  in  very  long  lengths  and 
so  incorporated  in  the  structure,  reducing  the  number  of  joints  necessitated  by 
pin-connected  chords,  because  of  the  facilities  for  fabrication  and  the  necessity 
of  making  the  joints  at  panel  points  for  the  proper  connection  of  the  laterals, 
which  is  immaterial  when  one  is  dealing  with  riveted  sections. 

The  suggestion  of  a slight  inclination  of  the  truss  might  be  objected  to 
on  the  ground  of  difficult  lateral  connections,  but  this  objection  is  more 
imaginary  than  real,  as  was  demonstrated  in  the  St.  Croix  River  Arch.*  Like 
Mr.  Lindenthal,  the  writer  appreciates  the  added  advantage  from  the  stand- 
point of  stiffness  which  some  indeterminate  structures  present,  but  this  may 
be  secured  with  the  indeterminateness  of  the  frame  largely  reduced  for  tempera- 
ture and  settlement,  as  was  done  in  the  structure  noted.  The  adoption  of  the 
riveted  sections  throughout  in  the  simple  span  permits  partial  erection  as  a 
cantilever,  adapting  the  design  to  conditions  under  which  the  pin-connected 
frame  is  at  a disadvantage. 

It  is  generally  assumed  that  the  continuous  bridge  has  some  inherent 
advantages  from  the  standpoint  of  stiffness,  as  compared  with  the  simple 
span.  If,  however,  the  economic  forms,  and  maximum  deflections  are  com- 
pared, this  will  not  be  found  to  be  true,  as  maximum  deflection  with  the 
continuous  bridge  occurs  when  some  of  the  spans  are  loaded  and  others  un- 

* Transactions,  Am.  Soc.  C.  E.,  Vol.  LXXV  (1912  f*  p.  1. 


960 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


loaded,  and  with  its  smaller  depth  at  mid-span,  with  partial  restraint  only 
at  the  support,  and  with  its  smaller  chord  section,  the  maximum  deflection  will 
be  found  to  be  greater  than  with  the  economically  designed  simple  span.  The 
difference,  although  in  favor  of  the  simple  span,  is  insufficient  to  offset  material 
economy  did  that,  in  fact,  pertain  to  the  continuous  bridge. 

Diverse  Laws  of  Economic  Chord  Inclination  in  Simple  and  Continuous 
Spans. — As  the  apportionment  of  the  efficiency  of  inclination  of  the  inclined 
chord  in  the  simple  span  is  as  the  cosine  of  its  angle  of  inclination  in  resist- 
ing horizontal  deformation  of  moment,  and  the  sine  of  its  angle  of  inclination 
in  resisting  the  vertical  deformation  of  shear,  its  efficiency  in  resisting  shear 
and  moment  is  as  the  secant  of  its  angle  of  inclination  is  to  unity,  compared 
with  horizontal  chords  on  a unit  weight  basis. 

Because  of  the  reverse  sign  of  the  bending  moment  in  the  cantilever  parts 
of  the  continuous  span,  there  is  a reversal  in  this  law  of  economic  efficiency. 
Take,  for  example,  the  member  of  Uls  to  U14.  in  the  author’s  continuous 
bridge  design.  For  negative  moment,  its  efficiency  in  resisting  horizontal 
moment  deformation  is  as  the  cosine  of  its  angle  of  inclination.  Its  efficiency 
in  resisting  vertical  shear  is  likewise  as  the  sine  of  its  inclination,  but  it 
carries  that  shear  vertically  a longer  distance  upward  from  the  point  of  reac- 
tion, L20,  thereby  increasing  the  material  necessary  to  support  it,  instead  of 
decreasing  the  material  necessary  to  support  the  shear,  as  is  the  case  with  the 
inclined  chord  where  the  moment  is  positive.  Accordingly,  the  cross-section 
of  2718-Z714  presents  a total  efficiency  in  resisting  combined  shear  and  moment 
of  an  amount  equal  to  the  cosine  of  the  angle  of  inclination  instead  of  the 
secant  of  the  angle  of  inclination,  as  is  the  case  with  the  inclined  chord  of 
the  arched  simple  truss  span. 

It  is  true  that  this  inclination  reduces  the  section  required  in  the  member, 
Uls-U^  so  that  the  economies  of  inclination  are  the  algebraic  sum  of  the 
plus  and  minus  savings  instead  of  the  consecutive  positive  summation,  as 
with  inclined  chords  in  the  simple  truss  span. 

The  Latitude  of  Compromise  of  the  Divergent  Economic  Requirements  of 
Floor  and  Truss  Panels  Unfavorable  to  the  Continuous  Span. — In  the  fore- 
going discussion,  it  has  been  noted  that  truss  triangulation  frequently  con- 
flicts with  economic  floor  paneling.  Thus,  comparing  from  the  standpoint 
of  the  simple  span  suggested,  the  bending  moment  of  the  four  lines  of  stringers 
is  70%  greater  in  Mr.  Lindenthal’s  continuous  truss  than  in  the  simple  truss 
diagram  suggested  by  the  writer.  The  dead  load  bending  moment  is  about 
100%  greater;  whereas,  conversely,  beam  shear  and  bending  moment  of  all  the 
beams  is  approximately  10%  greater  for  the  simple  span  than  for  the  con- 
tinuous span  partly  offset  by  the  greater  dimensions  laterally  of  the  chords 
which  would  naturally  be  used.  Accordingly,  the  range  for  compromise  ad- 
justment is  the  difference  between  one  clear  dimension  for  the  simple  span 
against  two  shorter  dimensions,  that  is,  the  cantilever  arm  and  the  suspended 
span  in  the  continuous  truss  of  two  spans,  or  three,  if  the  span  is  an  inter- 
mediate one,  with  an  economic  location  for  the  point  of  inflection  inhar- 
monious with  favor^ftle  panels  for  either  cantilever,  suspended  span,  or  floor. 


DISCUSSION  ON  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER  961 

This  is  a practical  disadvantage  of  no  small  importance,  which  should  not 
be  overlooked  in  a theoretical  survey  of  the  two  types  of  construction.  Gen- 
eral experience  with  continuous  draw-spans  gives  the  practical  engineer  a 
better  basis  for  a comparison  of  the  stiffness  of  two-span  continuous  struc- 
tures with  single  span  structures  of  the  dimension  of  the  length  of  the  arm, 
than  the  relations  of  bending  and  moment  forces  presented  in  works  on  bridge 
design,  and  from  this  experience  conclusions  regarding  stiffness  are  diametric- 
ally opposed  to  those  customarily  drawn  from  incomplete  theory  of  resistance 
based  on  moment  and  neglecting  shear. 

Among  engineers,  experienced  in  the  art  of  bridge  construction,  few  are 
egotistical  enough  to  assume  ability  to  design  the  most  economical  frame  possi- 
ble to  devise,  yet  it  would  seem  that  a thorough  discussion  of  theoretical  prin- 
ciples should  lead  to  less  divergence  of  opinion.  With  theoretical  treatises 
on  continuous  bridge  construction  estimating  from  moment  distribution  an 
economy  of  25  to  40%  in  the  material  required  for  the  continuous  truss 
bridge,  and  practical  experience  and  conscientious  design  apparently  indicating 
a lack  of  economy  of  35%  for  a two-span  continuous  structure  to  25%  for 
a four-span  continuous  structure,  from  consideration  of  essential  provision 
for  combined  shear  and  moment  and  the  relations  indicated  by  the  constant 
of  the  moment  magnitude  equations,  as  well  as  numerical  values  of  the  three- 
moment  equations,  there  appears  indeed  ample  room  for  harmonization  of 
book  theory  and  practical  experience  as  it  is  viewed  by  those  who  take  the 
negative  side  of  the  economic  question  and  ample  room  for  explanation  on 
the  part  of  those  who  assume  the  affirmative  side.  Undoubtedly,  the  author’s 
closing  discussion  in  the  affirmative  will  be  interesting  and  instructive. 

In  closing  this  discussion,  the  writer  thanks  Mr.  Lindenthal  for  the  pres- 
entation of  a most  interesting  and  valuable  paper,  which  skillfully  treats  of 
many  practical  questions  and  discloses  meritorious  details  in  advance  of 
current  practice.  Preference  for  the  continuous  bridge  of  moderate  span 
differs  from  the  majority  opinion  of  American  bridge  engineers,  because  of 
lack  of  demonstrated  economy  on  a scientific  mathematical  or  design  basis. 

T.  Kennard  Thomson,*  M.  Am.  Soc.  C.  E. — Beference  has  been  made  to  the 
danger  of  placing  falsework  in  the  Ohio  Biver,  which  reference  is  fully  appre- 
ciated by  the  speaker,  as  he  was  Engineer  of  Bridges  for  the  Ohio  Biver  Divi- 
sion of  the  Norfolk  and  Western  Bailroad  when,  in  1890-91,  the  Kenova  Bridge 
was  built  a few  miles  above  the  site  of  the  Sciotqyille  Bridge.  At  Kenova, 
the  records  showed  a low-water  depth  of  6 ft.  and  a high-water  depth  of  106  ft. 

The  author  has  called  attention  to  the  desirability  of  rock  foundations  for 
continuous  girders.  Any  departure  from  this  fundamental  should  ofily  be 
adopted  after  the  most  careful  consideration.  For  example,  a sufficient  num- 
ber of  piles  might  be  driven  to  carry  safely  several  times  the  designed  load; 
but  unexpected  contingencies  may  divert  a river  in  such  a manner  that  these 
foundations  would  be  seriously  imperiled  by  undermining.  Again,  the  teredo, 
which  had  nevef  been  known  in  the  locality  before,  might  'obtain  access  to 
the  piles. 


* Cons.  Engr.,  New  York  City. 


962 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


Some  years  ago,  it  would  have  been  considered  safe  to  cut  piles  off  30  or 
40  ft.  under  water,  as  the  teredo  was  only  supposed  to  find  access  to  the  piles 
between  high  and  low  water.  About  twelve  years  ago,  however,  the  speaker 
was  retained  to  report  on  a highway  bridge  at  Fall  River,  Mass.,  where  one 
end  of  a pier  had  dropped  2 ft.  in  one  night.  A pile  head  was  cut  off  and 
brought  up  with  live  teredo  and  also  limnoria,  both  actively  boring. 

The  piles  had  been  cut  off  30  or  35  ft.  below  the  surface  of  the  water  and 
4 ft.  of  timber  grillage,  carrying  masonry  pier,  had  been  sunk  on  top  of 
these  piles.  The  bridge  had  been  completed  just  two  years  prior  to  the  col- 
lapse of  the  pier.  As  the  piles  were  cut  off  at  such  great  depth,  and  as  there 
was  a sewer  discharging  within  150  ft.  of  the  pier,  it  would  have  been  con- 
sidered safe  against  the  ravages  of  the  teredo. 

The  speaker,  however,  has  never  been  able  to  satisfy  himself  as  to  whether 
the  teredo  and  the  limnoria  obtained  access  to  the  piles  after  they  were  driven, 
or  while  they  were  floating  on  the  surface  of  the  water  before  being  driven. 
In  any  event,  great  care  should  be  exercised  against  allowing  piles  to  float 
in  teredo-infested  water  before  driving. 

As  the  Fall  River  Bridge  did  not  have  continuous  trusses,  no  serious 
damage  was  done.  A coffer-dam  was  built  around  the  pier  and  concrete  was 
forced  under  the  grillage  around  the  old  pile-caps  and  brought  up  outside 
the  pier,  above  the  timber  grillage  line,  to  form  a new  support  for  the  bridge 
and  to  prevent  any  further  damage  by  the  teredo.  The  steelwork  was  then 
jacked  back  to  its  original  position  on  a new  bridge  seat. 

Charles  Evan  Fowler,*  M.  Am.  Soc.  C.  E.  (by  letter). — The  present  era 
of  bridge  building  may  well  be  termed  the  long-span  bridge  era,  as  it  is  now 
possible  to  span  wide  rivers,  estuaries,  or  canyons  more  scientifically  and 
economically  than  at  any  past,  or,  perhaps,  any  relatively  near  future,  period. 
The  Sciotoville  Bridge  is  a striking  example  as  to  what  may  be  accomplished 
by  the  use  of  continuous  bridges.  It  is  the  longest  of  that  type  ever  con- 
structed and  now  gives  to  America  the  proud  distinction  of  having  the  longest 
spans  for  every  type  of  bridge  construction,  namely,  the  Sciotoville  Continuous 
Bridge,  the  Hell  Gate  Arch,  the  Quebec  Cantilever,  the  Williamsburgh  Sus- 
pension, the  Metropolis  Simple  Truss  Span,  and  the  Willamette  River  Draw- 
Bridge. 

The  piers  of  the  Sciotoville  Bridge  are  illustrative  as  to  what  should  be 
done  in  the  reinforcing  of  monolithic  concrete  piers,  not  only  for  the  preven- 
tion of  cracks,  but  as  providing  a strong  protective  shell  for  resisting  the 
impact  from  ice,  logs,  scows,  or  collisions  from  steamboats.  For  this  purpose, 
the  writer’s  practice  has  been  to  use  wire  cloth,  placed  3 or  4 in.  inside  the 
surface  of  the  pier,  and  it  is  economical  and  effective.  The  care  exercised  in 
obtaining  a proper  foundation  for  these  piers  is  to  be  commended,  as  it  is  a 
fundamental  and  vital  matter  in  the  building  of  long-span  bridges. 

The  appearance  of  the  bridge  is  peculiarly  pleasing  when  one  considers  that 
it  is  a two-span  structure,  with  outlines  formed  by  straight  lines.  This  satis- 
fying feature  is  due  to  proper  depths  of  trusses  and  a strictly  symmetrical  struc- 


* Cons.  Engr.,  New  York  City. 


DISCUSSION  ON  SCIOTOVILLE  BRIDGE  OVER  THE  OHIO  RIVER 


963 


ture.  The  system  of  trussing  adopted  is,  also,  without  question  the  best  that 
could  have  been  selected  and  one  well  adapted  to  meet  the  problems  that  arose 
in  the  method  of  erection.  These  results  were  evidently  achieved  as  a result  of 
a trained  judgment  and  careful  investigation.  It  is  no  surprise,  therefore, 
to  know  the  final  outcome  as  to  the  economy  and  efficiency  of  the  structure. 

The  unit  stresses  used  in  making  the  design  should  receive  careful  study 
by  the  Special  Committee  on  Specifications  for  Bridge  Design  and  Construc- 
tion, and  all  engineers  having  to  do  with  the  design  of  steel  bridges  of  any 
magnitude,  as  engineers  can  no  longer  be  so  wasteful  of  the  resources  of 
Nature  as  they  have  been  in  the  past.  The  loading  adopted  undoubtedly  will 
prove  heavy  enough  for  the  future,  as  the  uniform  train  load  was  the  governing 
one  for  the  main  truss  members,  and  with  the  margin  allowed  inside  the  elastic 
limit  of  the  material,  the  floor  and  primary  truss  members  will  probably  never 
be  wanting  in  strength.  The  use  of  riveted  construction  throughout  is  to  be 
commended,  as  the  structure  in  consequence  thereof  is  much  stiffer  and  more 
lasting,  thus  nullifying  the  slight  decrease  in  cost  that  the  use  of  eye-bars  would 
have  effected. 

The  salient  points  of  this  structure,  as  well  as  of  this  type  of  bridge,  have 
been  so  well  covered  in  the  paper  that  the  writer  will  not  comment  on  them, 
but  engineers  should  study  them  carefully  and  endeavor  to  absorb  those  larger 
problems  of  design  which  have  been  solved  so  well. 

J.  E.  Greiner,*  M.  Am.  Soc.  C.  E.  (by  letter). — The  author  mentions 
those  early  engineers  kwho  had  the  “genius  that  originates  as  distinguished 
from  routine  which  merely  imitates.”  It  may  be  said  also  that  in  every 
structure  of  importance  designed  by  Mr.  Lindenthal  there  is  evidence  of  this 
genius  which  originates.  Each  of  his  structures  is  practically  a new  creation 
as  compared  with  the  routine  and  stereotyped  bridges  throughout  the  United 
States. 

The  Sciotoville  Bridge  is  no  exception.  It  is  a daring  and  handsome 
structure,  decidedly  “Lindenthalic”  in  all  its  features,  and  designed  to  carry 
Cooper’s  E-60  loading.  No  one  will  question  its  strength  or  its  adequacy  for 
any  load  that  will  ever  pass  over  it,  but  one  may  well  wonder  whether  this 
bridge  designed  for  E-60  loading  can  be  rated  as  an  E-60  structure.  The 
customary  rating  of  railroad  bridges  is  based  on  the  ratio  of  the  working 
stress  to  the  ultimate  strength,  which  ratio  according  to  the  American  Railway 
Engineering  Association  specifications  is  16:60,  or  0.267.  The  ratio  used  by 
Mr.  Lindenthal  is  20:66,  or  0.303,  which  is  13.5  higher  than  the  standard  and 
places  this  structure  in  the  E-53  and  not  in  the  E-60  class. 

The  author’s  compression  as  well  as  his  impact  formulas  are  quite  at  vari- 
ance with  general  practice.  He  may  be  right,  and  all  other  engineers  may  be 
wrong.  It  is  admitted  that  working  stresses  and  column  and  impact  formulas 
always  have  invited  juggling,  and  probably  always  will  be  subjects  for  the 
engineer’s  dicta  when  he  has  such  a prerogative.  There  are,  of  course,  standards 
for  these  stresses  and  formulas,  but  no  one  would  expect  Mr.  Lindenthal  to 
give  much  consideration  to  such  standards.  He  establishes  his  own  standards. 

* Cons.  Engr.,  Baltimore,  Md. 


964  DISCUSSION  ON  SCIOTOYILLE  BRIDGE  OYER  THE  OHIO  RIVER 

If  he  is  correct  in  rating  his  Sciotoville  Bridge  as  an  E-60  structure,  then  all 
the  railroad  bridges  built  for  such  a loading  in  accordance  with  the  American 
Railway  Engineering  Association  specifications  are  E-68  bridges,  and  if  the 
Association’s  E-60  bridges  are  really  such,  then  the  Sciotoville  Bridge  is  only 
an  E-53  bridge. 

D.  B.  Steinman,*  M.  Am.  Soc.  C.  E.  (by  letter). — The  continuous  truss 
is  an  excellent  bridge  type,  offering  decided  advantages  (under  suitable  con- 
ditions) over  all  other  forms  of  construction.  Its  general  adoption  for  fixed 
spans  has  long  been  retarded  by  prejudices  based  on  erroneous  notions;  but 
the  successful  execution  of  several  notable  examples  in  the  last  few  years 
(Sciotoville,  1917;  Allegheny  River,  1918;  Nelson  River,  1918;  Cincinnati, 
1922)  has  served  to  dispel  these  prejudices,  and  the  continuous  truss  has  become 
established  as  an  important  type  in  American  bridge  practice. 

In  comparison  with  simple  spans,  the  continuous  bridge  offers  the  same 
advantages  as  the  cantilever,  namely: 

1.  — Economy  of  material. 

2.  — Suitability  for  erection  of  one  or  more  spans  without  falsework. 

In  addition,  the  continuous  bridge  is  superior  to  the  cantilever  in 

3.  — Rigidity  under  traffic. 

4.  — Less  abrupt  stress  changes  under  traffic. 

5.  — Elimination  of  expensive  and  troublesome  hinge  details. 

6.  — Less  extra  material  or  hazard  in  erection.  « 

7.  — Safety  of  the  completed  structure. 

The  results  of  economic  comparisons  between  continuous  and  simple  spans 
will  be  materially  affected  by 

1.  — The  length  of  spans. 

2.  — The  system  of  web  bracing  used. 

3.  — The  specification  provision  for  reversal  of  stresses. 

The  relative  economy  of  the  continuous  type  increases  with  the  length  of 
span  or,  in  general,  with  the  ratio  of  dead  load  to  live  load.  It  is  wrong  to 
draw  a general  conclusion  against  the  economy  of  continuous  bridges  based 
on  a comparison  for  small  spans  (as  Bender  did  in  his  book  “Continuous 
Bridges”  in  1876). 

Furthermore,  for  a correct  economic  comparison,  the  most  suitable  system 
of  web  bracing  should  be  assumed  for  each  respective  type;  a Pratt  or  Petit 
system  may  be  most  economical  for  the  simple  spans,  but  a Warren  system 
will  generally  yield  the  best  results  for  the  continuous  truss. 

Finally,  the  results  of  the  economic  comparison  may  be  upset  by  the 
unscientific  practice  of  imposing  a stringent  reversal  clause;  these  reversal 
clauses  as  applied  to  the  proportioning  of  main  sections  are  relics  of  exploded 
fatigue  theories,  and  should  find  no  place  in  modern  specifications  for  long 
span  bridges. 

A proper  comparison  with  corresponding  simple  spans  will  generally  show 
a substantial  saving  of  material  in  favor  of  the  continuous  structure.  It  is 


* Cons.  Engr.,  New  York  City. 


DISCUSSION  ON  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER  965 

difficult  or  impossible  to  arrive  at  reliable  conclusions  in  this  question  from 
abstract  argument  or  theoretical  considerations. 

For  purposes  of  comparison,  the  writer  has  made  careful  estimates  of  the 
weight  of  simple  spans  of  775  ft.,  based  on  detailed  calculations  of  all  stresses 
and  sections.  The  live  load  was  E-60  (on  two  tracks),  and  designs  were  made 
both  for  LindenthaTs  specifications  and  for  the  American  Railway  Engineering 
Association  specifications.  The  results  were  as  follows: 

Weight  of  two  trusses,  in  pounds  per  linear  foot: 


1 550-ft.  Sciotoville  Bridge 12  880  = 100% 

775-ft.  Simple  span  (LindenthaFs  specifications) 15  300  = 119% 

775-ft.  Simple  span  (A.  R.  E.  A.  specifications) 17  650  = 137% 

Total  steelwork,  in  pounds  per  linear  foot : 

1 550-ft.  Sciotoville  Bridge 17  100  = 100% 

775-ft.  Simple  span  (LindenthaFs  specifications)  20  300  = 119% 

775-ft.  Simple  span  (A.  R.  E.  A.  specifications) 23  000  ==  134% 


The  foregoing  weights  of  simple  spans  do  not  include  the  extra  metal  which 
would  have  been  required  for  the  erection  of  the  channel  span  by  the  cantilever 
method. 

These  figures  bear  out  Mr.  Lindenthal’s  claim  of  a saving  of  20%  in  the 
weight  of  the  steel  by  the  adoption  of  the  continuous  type  for  the  Sciotoville 
Bridge. 

According  to  comparative  studies  made  by  Winkler,  the  saving  for  con- 
tinuous bridges  of  two,  three,  and  four  spans  is  16,  19,  and  21%,  respectively, 
when  the  span  length  is  about  300  ft. ; and  20,  24,  and  28%,  respectively,  when 
the  span  length  is  about  500  ft. 

Generally,  however,  the  economy  of  material  is  a secondary  consideration 
in  the  adoption  of  the  continuous  type,  the  deciding  advantages  being  the 
convenience  of  cantilever  erection  and  the  increased  stiffness  of  the  structure. 

The  following  conditions  are  particularly  favorable  to  the  economy  and 
efficiency  of  the  continuous  bridge  in  comparison  with  other  types  I 

1.  — Long  spans. 

2.  — High  ratio  of  dead  to  live  load. 

3.  — Good  foundations. 

4.  — Piers  of  moderate  height. 

5.  — Moderate  truss  depth. 

6.  — Spans  approximately  equal. 

7.  — Cantilever  erection. 

When  the  spans  are  long,  the  other  requirements  assume  minor  importance. 

Both  the  economy  and  rigidity  of  the  continuous  type  increase  with  the 
number  of  spans,  but  the  gain  beyond  three-  or  four  spans  is  insignificant. 
Moreover,  a larger'  number  of  spans  would  create  difficulty  in  providing  for 
expansion  on  account  of  the  great  length  between  expansion  joints.  Another 
objection  is  the  greater  number  of  supports  at  which  jacking  operations  would 
be  required  during  erection  for  the  adjustment  of  the  reactions.  (In  a two- 
span  bridge,  only  one  support  out  of  three  requires  jacking  adjustment;  in  a 
five-span  bridge,  four  supports  out  of  six  would  require  jacking,  and  the  opera- 


966  DISCUSSION  ON  SCIOTOYILLE  BRIDGE  OYER  THE  OHIO  RIVER 

tion  would  be  more  complicated.)  For  these  considerations,  the  number  of 
spans  in  a continuous  group  is  generally  limited  to  three  or  four. 

In  a two-span  bridge,  the  requirements  of  economy  as  well  as  of  appearance 
are  best  satisfied  by  making  the  two  spans  equal  in  length.  In  bridges  of  three 
or  more  spans,  a symmetrical  layout  is  also  desirable  for  appearance  and  for 
shop  economy.  In  a three-span  bridge,  the  economic  ratio  of  spans  is  approxi- 
mately 7 : 8 : 7 ; but  considerable  variations  from  these  proportions  will  not 
materially  affect  the  economy.  In  a four-span  bridge,  the  economic  ratio  of 
spans  is  approximately  3 : 4 : 4 : 3 ; but  these  proportions  may  also  be  varied 
considerably  without  materially  affecting  the  economy. 

In  many  cases,  the  span  arrangement  is  determined  by  natural  conditions 
of  the  crossing  (or  by  the  desire  to  utilize  existing  piers)  rather  than  by 
economic  or  esthetic  considerations. 

The  effect  of  possible  pier  settlement  on  the  stresses  in  continuous  bridges 
has  been  grossly  over-estimated  by  former  writers  on  the  subject.  In  the 
case  of  the  Sciotoville  Bridge,  according  to  the  writer’s  computations,  an 
excess  settlement  of  1 in.  at  the  end  support  would  produce  a relief  in  the 
end  reaction  amounting  to  15  000  lb.  This  is  only  0.6%  of  the  dead  load 
reaction,  or  0.3%  of  the  total  (D  -f-  L -f-  I)  reaction.  The  simultaneous 
increase  in  the  middle  reaction  would  be  30  000  lb.,  which  is  only  0.3%  of  the 
dead  load  reaction,  or  0.2%  of  the  total  (D  -f-  L -(-  1)  reaction  at  the  middle 
support.  An  excess  settlement  of  1 in.  at  the  middle  support  would  produce 
effects  equal  to  double  those  just  given,  but  opposite  in  sign.  The  middle 
reaction  would  be  relieved  60  000  lb.,  or  less  than  0.4%  of  the  total  (D  -j-  L -|- 1) 
reaction  at  the  middle  support.  It  is  evident  from  these  figures  that  any 
ordinary  settlement  of  the  piers  would  affect  the  stresses  in  the  structure  to 
so  small  an  extent  as  to  be  negligible. 

A former  objection  to  the  continuous  bridge  was  its  static  indeterminate- 
ness. With  modern  methods  of  design  and  construction,  however,  it  is  pos- 
sible to  know  the  exact  stresses  in  a continuous  structure  for  any  given  con- 
ditions; the  uncertainties  can  be  made  as  small  as  in  simple  spans  and  the 
extra  labor  of  the  computations  is  trifling  in  itself,  as  well  as  in  comparison 
with  the  advantages  to  be  derived. 

The  method  of  calculation  developed  for  the  Sciotoville  Bridge  was  de- 
scribed by  the  writer  in  an  article  entitled  “The  Elastic  Curve  Applied  to  the 
Design  of  the  Sciotoville  Bridge^’.*  The  entire  work  of  calculating  the  elastic 
curve  by  this  method  requires  only  2 or  3 hours  at  the  most.  After  the  elastic 
curve  is  determined,  the  remainder  of  the  design  is  essentially  the  same  as 
for  a simple  structure. 

In  the  case  of  the  Sciotoville  Bridge,  three  successive  designs  were  made : 

1.  — Preliminary  approximate  design,  treating  the  truss  as  a beam  with 
constant  moment  of  inertia. 

2.  — More  exact  design,  allowing  for  the  variation  in  moment  of  inertia  but 
with  the  web  members  neglected. 

3.  — Final  exact  design,  allowing  for  the  variation  in  moment  of  inertia 
with  the  contributions  of  all  the  members  included. 


Engineering  Record,  August  28th,  1915. 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


967 


The  sections  obtained  in  the  first  approximation  were  used  as  a basis  for 
the  succeeding  designs.  The  elastic  ordinates  for  the  three  assumptions,  also 
for  the  assumption  of  triangular  variation  of  I,  are  compared  in  Table  2. 


TABLE  2. — Comparison  of  Elastic  Curves,  Sciotoville  Bridge. 


Panel  point 

(i) 

X 

T 

(2) 

Assumption 

I = constant 

(3) 

Web  members 
neglected 

(4) 

All  members 
included 

(5) 

Assumption, 
triangular 
variation  of  I 

(6) 

A 0 

0 

1.000 

1.000 

1.000 

1.000 

2 

0.1 

0.875 

0.871 

0.876 

0.855 

4 

0.2 

0.752 

0.744 

0.754 

0.720 

6 

0.3 

0.632 

0.623 

0.632 

0.595 

8 

0.4 

0.516 

0.505 

0.509 

0.480 

10 

0.5 

0.406 

0.393 

0.392 

0.375 

12 

0.6 

0.304 

0.287 

0.287 

0.280 

14 

0.7 

0.211 

0.193 

0.192 

0.195 

16 

0.8 

0.128 

0.114 

0.115 

0.120 

18 

0.9 

0.057 

0.053 

0.055 

0.055 

B 20 

1.0 

0 

0 

0 

0 

Arfifl,  A B 

4.381 

4.283 

0.717 

4.312 

4.175 

Area  BC 

0.619 

0.688 

0.825 

Sura  of  areas  . . . 

5.000 

5.000 

5.000 

5.000 

Table  2 is  useful  inasmuch  as  its  values  can  be  adopted  for  the  prelimi- 
nary designs  of  other  structures,  thereby  saving  time  and  labor.  For  a struc- 
ture similar  in  general  outline  to  the  Sciotoville  Bridge,  the  values  in  Column 
5 should  be  used.  For  girders  and  trusses  with  parallel  chords,  the  values  in 
Column  3 would  probably  be  a closer  approximation. 

The  assumption  of  triangular  variation  of  moment  of  inertia  (assuming  1 
to  vary  as  the  ordinates  of  a triangle  from  zero  at  the  ends  to  a maximum  at 
the  intermediate  support)  may  also  be  recommended  as  a basis  for  preliminary 
or  approximate  design.  This  assumption  will  generally  represent  the  actual 
variation  of  7 in  a two-span  continuous  truss  about  as  well  as  the  assumption 
of  constant,  I;  moreover,  it  yields  results  of  striking  simplicity.  The  elastic 
curves  are  parabolas,  and  other  convenient  relations  obtain.  Instead  of  the 
more,  laborious  “Theorem  of  Three  Moments”,  one  is  able  to  use  the  following 
simple  formulas  for  the  moment  over  the  middle  support.  For  concentrated 
loads : 

*. = - 4 2 * 

in  which  M is  the  simple-beam  bending  moment  produced  by  each  con- 
centrated load  at  its  own  point  of  application.  For  continuous  or  concentrated 
loads : 

M2  = — — (Al  + A2) 

in  which  A1  is  the  area  of  the  simple-beam  moment  diagram  in  one  span,  and 
A 2 is  the  area  in  the  other  span. 


Scyiare  inches 


968  DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 

P 

In  making  preliminary  assumptions  as  to  distribution  of  dead  load, 
variations  of  sections  of  truss  members,  and  variations  of  moment  of  inertia, 
the  corresponding  distribution  graphs  for  the  Sciotoville  Bridge  may  be  of 
assistance.  With  this  object  in  view,  the  writer  has  prepared  Fig.  26  which 
shows,  by  graphs,  the  distribution  of  material  in  the  Sciotoville  spans. 


DISTRIBUTION  OF  DEAD  LOAD  UNITS  =1000  LB.  (PAMEL  LOAD  PER  TRUSS) 


Fig.  26. 

Certain  improvements  in  distribution  of  material,  with  possible  saving  in 
total  weight,  may  be  secured  by  intentionally  building  the  middle  support 
lower  than  the  end  supports  by  a predetermined  amount.  The  excess  of  middle 


Square  inches 


DISCUSSION  ON  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER  969 

reaction  over  end  reactions  can  thus  be  somewhat  relieved,  and  the  greatest 
negative  and  positive  moments  can  be  equalized.  In  a two-span  girder  of 
equal  spans  and  constant,  I it  will  be  advantageous  to  lower  the  middle  sup- 
port an  amount  defined  by : 

D = (1.9  w + p)  14g£  j 

in  which  w = the  dead  load,  and  p = the  live  load  per  linear  foot.  This  will 
reduce  the  negative  moment  over  the  middle  support  from  about  16  to  31% 
(depending  on  the  ratio  of  w : p)  and  will  increase  the  maximum  positive 
moment  within  the  span  to  an  equal  value.  For  the  Sciotoville  Bridge,  the 
necessary  camber  or  lowering  corresponding  to  this  formula  would  be  about  14 
in.  This  would  have  reduced  the  maximum  required  section  (over  the  middle 
support)  from  596  to  520  sq.  in.,  a reduction  of  76  sq.  in.;  and  it  would  have 
increased  the  mid-span  section  from  474  to  520  sq.  in.,  an  increase  of  46  sq.  in. 
Such  equalization  of  maximum  sections,  with  a reduction  of  13%  in  the  ex- 
treme heaviest  sections,  is  an  advantage  worth  considering  in  future  designs. 

In  common  with  other  indeterminate  structures,  the  continuous  bridge 
offers  the  possibility  of  varying  the  distribution  of  stress  by  adjustment.  In 
the  case  of  the  Niagara  Railway  Arch  Bridge,*  it  will  be  recalled  how  Charles 
Evan  Fowler,  M.  Am.  Soc.  C.  E.,  secured  a favorable  readjustment  of  dead  load 
stresses  by  changing  the  thickness  of  the  shims  at  mid-span.  Similarly,  in  a 
continuous  bridge,  the  dead  load  stresses  may  be  redistributed  by  the  predeter- 
mined raising  or  lowering  of  one  or  more  supports.  This  may  be  done  during 
erection,  in  order  to  reduce  the  maximum  required  sections,  or  in  order  to 
secure  a more  favorable  distribution  of  material  to  resist  erection  stresses;  or 
the  jacking  operation  may  be  resorted  to  after  the  bridge  has  been  standing  for 
some  time  in  order  to  relieve  members  which,  for  any  reason,  may  be  found 
to  be  overstressed. 

Three  notable  innovations  in  the  design  of  the  Sciotoville  Bridge  were  as 
follows : 

1. — The  adoption  of  U-shaped  floor-beams,  designed  as  inverted  arches. 

2 —The  adoption  of  lattice  sway-frames,  instead  of  the  usual  rigid  cross- 
frames. 

3. — The  initial  bending  of  the  members  to  neutralize  the  secondary  stresses. 

The  adoption  of  the  U-type  of  floor-beam  is  probably  without  precedent  in 
practical  bridge  design,  although  the  combination  of  conditions  warranting 
its  use  may  easily  occur  in  any  long  span  structure.  The  application  of  the 
U-shaped  floor-beam  is  indicated  in  any  structure  in  which  there  obtains 
limited  floor  depth  with  excessive  width  between  trusses.  This  combination  of 
conditions  renders  the  straight  type  of  floor-beam  uneconomical;  and  the 
second  condition,  from  considerations  of  clearance,  renders  the  U-type  prac- 
ticable. Both  these  conditions  obtained  in  the  Sciotoville  Bridge.  In  this 
structure,  in  order  to  secure  adequate  transverse  stiffness  against  wind  and 
lateral  forces,  the  length  of  floor-beam,  or  distance,  center  to  center  of  trusses, 
was  made  38  ft.  9 in.,  or  one-twentieth  of  the  span.  This  is  nearly  10  ft.  in 
excess  of  the  width  required  for  train  clearance,  this  excess  of  clearance  being  a 


Transactions , Am.  Soc.  C.  E.,  Vol.  LXXXIII  (1919-20),  p.  1919. 


970 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


consequence  of  the  unusual  length  of  span  for  a bridge  of  only  two  tracks.  The 
excessive  distance  between  the  truss  and  stringers  results  in  high  bending 
moments,  so  that  a floor-beam  depth  of  8.5  or  9.0  ft.  would  be  desirable  for 
economy.  Actually,  a depth  of  only  7.5  ft.  was  available.  Although  an  addi- 
tional 12  or  18  in.  of  height  would  have  given  lighter  floor-beams  and  stringers, 
it  could  not  be  secured  except  at  the  expense  of  raising  and  lengthening  a 
40-ft.  fill  nearly  2 miles  in  length  at  the  Kentucky  approach.  To  overcome 
the  disadvantage  caused  by  this  limitation  of  depth,  the  U-shaped  floor-beam 
was  devised.  This  design  yields  the  following  advantages : 

1.  — A material  saving  in  the  total  weight  of  floor-beam. 

2.  — A considerable  reduction  in  the  bending  moments,  thereby  avoiding 
some  of  the  difficulties  of  providing  extra  heavy  flange  sections. 

3.  — Increased  transverse  stiffness  of  the  bridge,  the  U -frame  becoming  an 
addition  to  the  sway-bracing. 

4.  — Elimination  of  the  secondary  stresses  in  posts  or  hangers  caused  by  the 
deflection  of  straight  floor-beams. 

5.  — Elimination  of  the  secondary  stresses  in  straight  floor-beams  due  to 
their  partial  constraint  at  the  ends. 

6.  — Increased  resistance  of  the  structure  to  vibration. 

In  the  Sciotoville  Bridge,  the  adoption  of  the  U-shaped  design,  according 
to  the  original  comparative  estimate,  reduced  the  maximum  live  load  moments 
by  39%  and  effected  a saving  of  9 000  lb.  of  steel  in  each  of  the  thirty-nine 
intermediate  floor-beams.  This  saving  in  weight  may  be  offset  somewhat  by 
increased  unit  cost  of  the  shop  work,  but  the  other  advantages  alone  would 
justify  the  adoption  of  the  U-shaped  floor-beam  wherever  adequate  lateral 
clearance  is  available. 

In  analyzing  the  stresses  in  the  U -frame,  it  is  important  to  make  proper 
allowance  for  the  shortening  of  the  bracing  strut  which  takes  up  the  hori- 
zontal thrust  of  the  inverted  arch. 

The  use  of  ordinary  sway-bracing  of  the  rigid  type  was  avoided,  in  the 
design  of  the  Sciotoville  Bridge,  on  account  of  the  high  stresses  which  such 
bracing  would  suffer  under  one-sided  loading  of  the  bridge.  Under  the 
extreme  case  of  one  track  of  one  span  and  the  opposite  track  of  the  other 
span  being  fully  loaded,  there  will  be  a difference  of  2 in.  in  the  mid-span 
deflections  of  the  two  trusses.  To  permit  this  unequal  deflection  without 
rupture,  the  usual  sway-frames  of  rigid  type  were  replaced  by  lattice-frames 
combining  strength  with  elastic  stiffness. 

The  scheme  for  neutralizing  the  high  secondary  stresses  in  the  structure  is 
another  feature  adding  distinction  to  the  Sciotoville  Bridge.  The  necessary 
erection  operations  were  calculated  with  unprecedented  care  and  thoroughness, 
and  the  measurements  of  jacking  forces  and  deflections  in  the  various  erection 
stages  afforded  an  excellent  check  on  the  calculations. 

The  Sciotoville  Bridge  is  a striking  example  of  scientific  design.  It  repre- 
sents an  unusually  intensive  application  of  engineering  theory  and  resourceful- 
ness to  the  determination  of  the  most  efficient  disposition  of  the  material  of  a 
structure,  and  to  the  rigorous  advance  planning  of  every  step  in  the  operations 
of  fabrication  and  erection. 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER  971 


Henry  H.  Quimby,*  M.  Am.  Soc.  C.  E. — The  speaker  recalls  that  forty 
years  ago  the  computers  of  a certain  bridge  company  made  simple  spans  of 
the  two  plate-girder  spans  of  a railroad  bridge  because  of  want  of  confidence 
in  their  figures  and  fear  of  some  indefinite  consequences  if  the  girders  were 
made  continuous  over  three  supports. 

Continuity  of  structure  is  an  economical  and  advantageous  principle  of 
design  and,  if  intelligently  used,  is  practical  and  safe.  In  bridges  of  several 
arched  spans,  it  has  been  applied  with  satisfactory  results — in  one  case  of  five 
spans,  the  steelwork  was  both  the  reinforcement  of  the  concrete  arch  ribs  and 
provision  for  the  erection  of  both  the  steel  and  the  concrete  without  falsework. 
In  another  bridge  that  had  a large  number  of  rod-reinforced  concrete  arches, 
reinforcing  rods  were  embedded  over  the  piers  as  the  tension  members  to 
constitute  the  first  voussoirs  cantilevers  for  carrying  the  forms  for  succes- 
sive voussoirs.  The  rods  were  left  exposed  for  a few  inches,  and  after  erection 
was  complete  they  were  cut  by  sawing.  The  tension  was  so  great  that  each 
rod  snapped  apart  when  partly  cut.  In  later  bridges,  both  with  structural 
shapes  and  screw  rods  as  tension  members  over  the  piers,  the  ties  were  per- 
mitted to  remain,  as  being  not  only  harmless,  but  possibly  contributory  to 
stiffness  as  well  as  to  stability. 

In  the  Sciotoville  Bridge,  the  effect  on  the  stresses  in  the  members,  which 
the  paper  states  would  be  produced  by  deformations  that  would  attend  certain 
settlements  of  piers,  is  surprisingly  small  in  view  of  the  great  height  of  the 
trusses.  As  so  much  settlement  can  hardly  be  imagined,  the  continuity  of 
truss  is  certainly  justified. 

The  method  of  erection  and  the  means  adopted  to  minimize  secondary 
stresses  are  interesting.  Both  must  have  been  expensive,  and  some  informa- 
tion regarding  the  cost  of  the  work  would  be  instructive.  The  plan  of  erection 
was  dictated  in  a measure  by  considerations  of  safety  under  the  attendant 
conditions  of  the  site  and  was  justified  by  its  success.  The  method  adopted 
for  reducing  secondary  stresses  was  bold  and  scientific,  but  must  have  been 
very  costly,  and  it  is  understood  to  have  involved  a great  deal  of  heavy 
drifting  and  reaming  to  get  the  holes  to  admit  the  rivets.  Can  the  author 
give  any  facts  regarding  these  points,  and  any  comparison  of  the  extra  cost 
of  the  work  as  done  with  the  cost  of  providing  additional  section  at  the 
critical  points  of  members  affected  by  secondary  stresses? 

Gustav  Lindenthal,!  M.  Am.  Soc.  C.  E.  (by  letter). — The  contention  made 
by  Mr.  Turner,  that  simple  girders  may  be  designed  with  no  more  or,  perhaps, 
with  less  steel  than  continuous  girders,  is  based  on  the  same  incomplete 
grounds  often  asserted  before.  Short  panels  to  reduce  floor  weights,  great 
height  between  chords  to  reduce  chord  sections,  and  curved  chords  to  reduce 
web  stresses,  are  all  long  known  devices  for  attaining  economy.  They  can 
be  used  in  both  the  simple  and  the  continuous  types,  and  also  in  the  cantilever 
type.  The  question  of  economy  can  hardly  be  settled  by  a comparison  of  strain 
lengths  in  the  several  types.  The  experience  of  bridge  designers  during  the 

* Chf.  Engr.,  Dept,  of  City  Transit,  Philadelphia,  Pa. 

f Cons.  Engr.,  New  York  City. 


972  DISCUSSION  ON  SCIOTO YILLE  BRIDGE  OVER  THE  OHIO  RIVER 

last  30  or  40  years  has  fairly  well  established  the  best  proportions  for  each 
type. 

The  theory  of  strain  lengths  originated  by  Charles  Bender  (who  was  per- 
sonally known  to  the  writer  45  years  ago),  seemed  at  the  time  a plausible  basis 
for  estimating  and  comparing  the  economy  of  bridge  and  roof  trusses,  fortified 
as  it  was  by  an  elegant  deduction  from  Clapeyron’s  theorem  of  deflections. 
With  simple  elements  of  loads  and  strains,  it  can  be  useful;  for  the  correct 
dimensioning  of  bridge  members,  however,  a greater  number  and  variety  of 
stresses  have  now  to  be  considered  than  were  thought  of  in  Bender’s  day.  To 
the  stresses  from  dead  and  live  load  must  be  added  the  various  combinations 
with  effects  of  impact,  traction  stresses,  wind  pressure,  secondary  stresses, 
etc.  The  theory  then  ceases  to  be  useful,  especially  so  in  bridge  frames  having 
heavy  members  with  reversible  stresses  (tension  and  compression),  as  in  con- 
tinuous and  cantilever  trusses. 

No  fact  on  the  strength  of  steel  is  more  firmly  established  from  practical 
tests  and  after  much  theoretical  travail  than  that  steel  and  wrought  iron  will 
safely  resist  without  deterioration  a nearly  infinite  number  of  variations  and 
reversions  of  stresses,  provided  the  unit  stress  remains  within,  say,  two-thirds 
of  the  elastic  limit.  To  take  advantage  of  this  fact  in  economic  bridge  design- 
ing, the  stresses  must  be  accurately  known.  This  is  not  always  feasible  with 
live  load  stresses,  some  of  which  are  dynamic,  but  are,  nevertheless,  assumed 
to  behave  statically  like  stresses  from  dead  or  other  quiescent  loads.  In  some 
members,  impact  stresses  may  exceed  the  statical  stresses  from  live  load  of  the 
same  or  opposite  sign.  The  theory  of  strain  length  under  all  these  conditions 
becomes  too  uncertain  for  the  a priori  comparison  of  economy  in  designs.  The 
only  reliable  comparison  in  any  given  case  is  on  the  basis  of  fully  worked 
out  stress  sheets,  complete  erection  schedules,  and  estimates  of  cost. 

If  two  spans  of  simple  girders  with  a height  of  of  the  span,  as  pro- 
posed by  Mr.  Turner,  should  show  greater  economy,  which  is  doubtful,  even 
with  alloy  steel,  then  there  is  no  reason  why  greater  height  could  not  also  be 
used  for  the  same  purpose  in  continuous  girders ; but  would  it  be  good  design- 
ing? Engineers  are  expected  to  build  good  bridges  economically.  That  does 
not  mean  freak  bridges  under  the  pretense  of  scientific  economy  which  too 
often  may  be  false  economy. 

In  this  double-track  bridge,  the  great  simple-girder  height  would  be  nearly 
four  times  the  width  between  girders.  A train  passing  over  the  bridge  would 
deflect  one  girder  more  than  the  other  by  several  inches.  That  would  throw  out 
the  top  of  the  girder  nearly  four  times  as  many  inches.  It  would  be  a very 
wabbly  structure,  possibly  a so-called  economic  design,  but  inferior  as  far  as 
behavior  under  use  is  concerned.  The  inclining  of  the  trusses,  as  suggested 
by  Mr.  Turner,  would  not  improve  it. 

In  the  continuous  girders,  the  greatest  height  (also  the  most  weight)  is 
over  the  middle  pier,  where  the  girders  cannot  deflect  horizontally  or  vertically. 
The  wind  bracing  between  the  chords  is  also  continuous.  The  four  con- 
tinuous girders  form  a long  rigid  box  of  great  stability,  open  at  the  ends, 
exposed  to  the  least  amount  of  vertical  and  horizontal  oscillation.  In  other 


DISCUSSION  ON  SCIOTO  VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


973 


words,  the  continuous  girders  are  in  every  way  stiffer  than  the  simple 
girders. 

A floor  with  28  panels  per  span,  as  proposed  by  Mr.  Turner,  in  place  of  20 
panels,  for  the  sake  of  saving  an  insignificant  quantity  of  steel  in  the  stringers, 
would  require  40%  more  handling  in  the  shops,  with  many  thousand  more  field 
rivets,  and  40%  more  field  operations  during  the  erection.  The  greater  cost 
of  field  labor  would  cancel  the  inconsiderable  saving  in  steel  for  stringers  of 
shorter  panels.  In  addition,  the  greater  compactness  of  long  panels  is  dis- 
carded. Owing  to  the  lighter  floor,  the  center  of  gravity  of  the  single  girder 
structure  is  higher  and  contributes  another  element  to  the  wabbliness  of  the 
bridge.  The  top  chord  panels  would  be  50%  longer  than  in  the  continuous 
girder  and  the  cross-sections,  therefore,  30%  larger,  thus  effacing  any  economy 
from  greater  height  of  trusses. 

The  simple  girders  would  require  considerable  extra  material  to  be  erected 
by  the  cantilever  method  over  the  large  river  opening  needed  during  erection. 
It  would  also  have  required  more  time  for  shifting  the  falsework  and  another 
material  yard  on  the  Kentucky  side,  which  was  not  available.  Compact,  short, 
well  braced,  compression  members  keep  the  chords  rigidly  in  line,  an  advantage 
largely  absent  in  the  simple  girder.  The  bridge  is  situated  in  a region  subject 
to  tornadoes  which  have  wrecked  one  or  more  bridges  over  the  Ohio  River. 
The  bracing  of  the  continuous  girders  can  be  made  better  and  stronger,  and 
they  are  thus  capable  of  offering  greater  resistance  to  wind  pressure. 

The  gravamen  of  Mr.  Greiner’s  discussion  is  that  the  capacity  of  the  bridge 
is  not  really  for  an  E-60  loading,  but  only  for  an  E-53  or,  say,  12%  lighter 
loads,  when  based  on  the  specification  of  the  American  Railway  Engineering 
Association.  The  A.  R.  E.  A.  specifications  are  intended  only  for  ordinary 
spans,  not  exceeding,  say,  350  ft.;  for  longer  spans  they  are  wasteful  in  the 
trusses.  This  fact  is  confirmed  by  a comparison  of  a few  sections  as  shown  in 
Table  3,  in  which  is  given  the  sectional  area  of  a number  of  typical  members  of 
the  Sciotoville  Bridge,  as  designed  according  to  the  writer’s  specifications  in 
comparison  with  those  required  by  the  latest  A.  R.  E.  A.  specifications  and  E-60 
loading.  Table  3 also  gives  a comparison  of  the  strength  of  these  members  for 
the  two  specifications,  based  on  the  fact  that  the  writer’s  specifications  require 
steel  at  least  13%  stronger  than  that  called  for  by  the  A.  R.  E.  A.  specifica- 
tions (minimum  yield  point,  35  000  against  30  000 ; ultimate  strength,  62  000 
against  55  000). 

The  statement  by  Mr.  Greiner  that  the  bridge  has  a live  load  rating  of  only 
E-53  is  shown  by  Table  3 to  be  unjustified  and  is  made  without  examination 
of  the  requirements  of  the  writer’s  specifications  other  than  the  basic  unit 
stress  (20  000),  which  may  mislead  superficial  readers. 

In  the  floor  system  and  floor  hangers  (as  in  short  spans  generally),  the 
writer’s  specifications  give  sectional  areas  up  to  25%  in  excess,  and  in  strength 
of  members  up  to  41%  in  excess  of  those  required  by  the  A.  R.  E.  A.  specifica- 
tions. That  makes  the  live  load  rating  for  the  floor  construction  in  this 
bridge  really  E-70  to  E-84  on  that  specification.  This  is  due  principally 
to  the  greater  impact  allowance  for  short  spans,  resulting  from  the  writer’s 
formula  for  impact,  which,  as  far  as  is  known  is  the  only  impact  formula 


974 


DISCUSSION  ON  SCIOTO VILLE  BRIDGE  OVER  THE  OHIO  RIVER 


deduced  from  well-known  facts  on  the  durability  of  steel  under  impact 
conditions.  It  is  simple  of  application  and  gives  rational  results  for  the 
shortest  and  the  longest  spans  alike.  This  advantage  adheres  also  to  the 
writer’s  specifications,  or  “Rules  of  Design”,  used  in  the  Hell  Gate,  Sciotoville, 
and  other  bridges.  These  specifications  give  well-balanced  working  stresses, 
insofar  as  uniform  durability  of  structure  is  concerned,  for  the  shortest  and 
the  longest  spans,  which  is  not  the  case  with  the  A.  R.  E.  A.  specifications. 


TABLE  3. 


Member. 

Existing  area, 
in  square  inches. 
Linden  thal 
design. 

Area,  in  square 
inches,  required 
by  A.  R.  E.  A. 
specification. 

Percentage  of 
excess  area, 
Lindenthal 
specification 
over  A.  R.  E.  A. 
specification. 

Percentage  of 
excess  strength, 
Lindenthal 
specification 
over  A.  R.  E.  A. 
specification. 

Stringer : 

Tension  flange,  net 

26.66 

24.0 

+11 

+25 

Compression  flange,  gross. . . 

30.58 

29.4 

+ 4 

+17 

Floor-beam  : 

Tension  flange,  net 

42.63 

34.1 

+25 

+41 

“ “ , gross 

46.32 

41.8 

+11 

+25 

Trusses : 

Top  chord  : 

U 6-J710,  gross 

435 

518 

—16 

— 5 

U10-L714,  gross 

317 

374 

—15 

— 4 

U14-U18,  net 

198 

187 

+ 5 

+18 

U18-U20,  net 

501 

579 

—13 

0 

Bottom  chord : 

L 4 -L  8,  net 

403 

404.1 

— 0 

0 

L12-L16,  net 

230.1 

255.1 

—10 

+ 2 

Diagonals : 

M 3-L  4,  net 

149.0 

154.6 

— 3.7 

9 

L 4-ilf  5,  gross 

150 

152.6 

— 1.6 

11 

TJ  6 -71/  71  gross 

104.5 

140 

—34 

—26 

L 8-M  9 net 

93 

124  0 

—33 

—25 

U10-M11,  gross 

224 

258  !o 

—13 

0 

U18-M19,  gross 

486.7 

655.0 

—25 

—15 

Main  hanger,  net . . 

90 

85.3 

+ 6 

+19 

Sub-hanger,  net 

49 

44.2 

+11 

+25 

The  sectional  areas  of  the  bottom  chord  (loaded  chord)  of  the  Sciotoville 
Bridge  are  nearly  the  same,  because  in  these  members  the  impact  allowance  is 
more  nearly  the  same,  for  both  specifications,  but  the  reduction  in  areas  which 
might  result  from  the  higher  unit  stresses  of  the  writer’s  specifications,  is 
offset  by  the  justified  greater  allowance  for  lateral,  wind,  and  brake  forces, 
which  may  co-exist  in  these  chords  with  the  dead  load,  live  load,  and  impact 
stresses. 

The  A.  R.  E.  A.  specifications  would  require  some  sections  of  the  top  chord 
and  main  web  members,  to  be  34%  larger,  and  in  strength  to  be  26%  greater. 
This  would  be  plainly  a waste  of  steel  due  to  the  low  unit  stresses  allowed  by  the 
A.  R.  E.  A.  specifications  (maximum  16  000  lb.  per  sq.  in.  in  tension  and  12  500 
lb.  per  sq.  in.  in  compression),  which  low  limits  are  not  justified  in  a bridge 
of  this  size.  The  waste  is  also  in  part  due  to  the  absurd  requirement  of  the 
A.  R.  E.  A.  specifications  that  members  subject  to  reversal  of  stress  shall  be 
proportioned  for  the  greater  stress  plus  50%  of  the  smaller  stress. 


DISCUSSION  ON  SCIOTO VI LLE  BRIDGE  OVER  THE  OHIO  RIVER 


975 


The  A.  R.  E.  A.  specifications  do  not  require  sufficient  metal  for  the  floor 
structure  and  for  short  spans  where  it  is  necessary,  because  these  structures  are 
stressed  to  the  violent  maximum  from  nearly  every  train,  and  they  require 
too  much  metal  for  the  truss  members  of  long  spans,  in  which  members,  the 
maximum  stresses  are  far  from  violent  and  rarely,  if  ever,  occur. 

The  belief  of  Mr.  Quimby  that  the  method  of  reducing  secondary  stresses 
was  costly  and  involved  a great  deal  of  heavy  drifting  and  reaming  in  order 
to  get  the  holes  to  admit  rivets  is  not  based  on  fact.  There  was  no  trouble  or 
extra  work  on  that  account  in  the  shop. 

Although  it  is  true  that  the  bending  of  the  members  in  the  field,  in  order 
to  make  the  rivet  holes  fit,  required  some  special  operations,  the  cost  of  such 
work  was  comparatively  small  and  was  fully  justified  by  the  advantage  gained. 
In  fact,  the  fabrication  and  erection  cost  of  the  bridge  per  pound  of  steel  was 
remarkably  low,  and  less  than  for  pin-connected  work,  as  proven  by  the  bids 
received  for  both  types  of  structures. 

The  discussion  by  Mr.  Steinman  is  a welcome  contribution  on  some  details 
and  features  already  mentioned,  in  the  main,  by  the  writer  in  his  paper, 
omitting  elaborations. 

The  conclusions  by  Professor  Winkler,  the  German  nestor  of  bridge  math- 
ematicians 45  years  ago,  mentioned  by  Mr.  Steinman,  on  the  economy  of  con- 
tinuous girders,  are  fully  confirmed  in  the  Sciotoville  Bridge.  French  and 
German  engineers  early  showed  much  less  hesitation  in  the  use  of  that  system 
than  American  engineers.  Almost  all  those  early  European  bridges  are  still 
in  good  condition,  although  railroad  loads  on  them  have  increased,  but  not’as 
much  as  in  America. 

Mr.  Steinman’s  idea  of  reducing  the  height  of  trusses  over  the  middle  pier 
and  increasing  the  height  at  mid-span,  would  not  be,  on  the  whole,  advantageous 
or  economical,  as  the  questionable  saving  of  metal  in  the  chords  would  be  out- 
balanced by  increased  sections  and  metal  in  the  web  members  toward  the  ends 
of  trusses.  There  would  also  be,  in  this  case,  the  objection  of  greater  erection 
stresses  and  too  much  deflection  during  erection,  with  greater  secondary  stresses 
in  cantilevering. 


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